As far as I'm aware developers have a choice of when/if games appear on GP, and what terms are acceptable when it gets placed there.
I'm not exactly thinking there is going to be a mass exodus away from the PS platform over this. If this was the plan for the top tier of the service, I'd think they had everyone onboard before they even announced. Could publisher response be aggressively negative down the line? Sure, depends on whether or not they think the demos are benefiting them or not.
I think that's fair. And, like I've been saying for several posts, if Sony were smart they'd offer some financial incentive to ensure companies really commit to these trails for the long haul.
Simplest approach is to reduce the 30% cut off the first half-million or so sales to say 25% or 20%. That would be good enough for virtually every single publisher; for specific games of a publisher they could adjust the quota to make it longer or shorter.
I assume that all of these publishers are testing these games before release and have a good idea what the general enthusiasm is before and after users have firsthand experience with the titles. I'm also assuming from the customer reviews that you see that just like film, some of these test out showing lower enthusiasm after playing than before and project less than favorable word of mouth. With that said, there will also be games where enthusiasm grows quite a bit after firsthand experience, I can see sales getting boosted there for sure.
As a player I'm completely fine with it. Even if I end up making my purchases on Xbox, I'm sure I'll spend time in the demos since my PSNow sub will be converted to the highest tier.
Speaking of reviews, I agree that allowing user reviews through PS+ itself for those playing these trails and games would be great. Not just because it could be a boon (or inhibitor, in case the trail or game is bad) to sales, but because (and this is just me personally speaking) in light of some of the shenanigans with certain game reviews on MetaCritic earlier in the year, it would be a great way for actual gamers and people within the ecosystem to express their thoughts on their played games and purchases.
That helps remove the over-reliance on review aggregates like MetaCritic, which as we've seen multiple times can be manipulated for pushing certain narratives, and puts more of power in the voice of the actual customer base. Or maybe, doing this could be done in tandem integrating it with aggregates like MetaCritic, so that they still hold some useful relevance.
What's also important for the test drive is any game that is server/MP heavy because nobody wants to commit $60 to a game with shitty launch servers. So hey, if the game sucks in that trial, then you just saved yourself $60. And if the game gets patched, then look into buying it later.
Interesting take; this does indirectly put pressure on studios (and their publishers) to keep the quality up. Though, some could also be deceptive and just put out a great trail preview for an otherwise crap game, who knows

.
If you publishers made more money when demoes were offered, they'd never have stopped offering them. Ergo, this will lead to decreased profits for publishers, who are now forced to use their games to fuel Sony's higher priced tier. If the first two hours of your game aren't an absolute banger, you're losing customers on PlayStation.
The publishers who released bad games or bad demos were the ones hurt by demos; good games or games with good demos had boosts in sales. I'm not understanding where this idea that demos hurt game sales as a whole came from. Do good trailers hurt movie ticket sales, or excite fans to want to watch them even more? Usually it's the latter. Same thing with good demos.
Now yes a good game can have a horrible demo and a trash game can have a fantastic demo, but how often did that really happen? And how would anyone even be able to gather the data to prove it were the case? If anything, I think the reason demos stopped being a thing was because thanks to the rise of streamers and gaming content creators online, demos just became less of a necessity. However, with costs of games generally going up they could be a useful thing at large once more.
That's the optimistic take. The pessimistic take is, demos went out of fashion because they became too time-consuming to make. If that's the case, then that problem doesn't suddenly get resolved just because Sony are mandating trails, because not every game is going to be able to just take any random 2-hour slice of finished gameplay and spin it off into a trail. Some may need to edit and patch things together to avoid spoilers, or may not be able to use the opening parts because they're too slow or uneventful and would leave a bad impression.
Those reasons are why there probably needs to be some type of universal, flat financial incentive for devs/pubs to really commit to trails over time, but we can only guess (and hope) Sony are working on that behind the scenes.
I just saw it mentioned that if it is a trial you might end up having to download a full game and have 2 hours to play it. At least with a demo it would be smaller and most likely wouldn't need a time limit either.
That could potentially be an issue for the end user, but only for 3P games that are not also available via PS Now. But like
yurinka
said, the game can be split up somewhat like a demo to build out other parts as desired.
It's a bit more work for the developer, though, and I'm interested how much more work that is compared to adding in trophies or achievements were back in the day (which apparently were also mandated by Sony & Microsoft for all 3P partners).
7. Potential loss in a % of game sales as players will think they got their "fill" out of the two hour trial, or end up deciding they don't need to buy the game, something they might have just bought on impulse if not presented with a 2 hour trial beforehand.
But by that logic you also have to accept the idea that GamePass, then, must in fact not lead to sales increases like it's been claimed, since in that service's case games are presented in their entirety for only the cost of the monthly sub. At least with 2-hour game trails, IF a person likes the game enough they are going to be inclined to buy it which means the publisher still gets their money.
And I know that GamePass has its way of offsetting potential lost sales via the payments they do on a per-game or per-dev/pub basis (not to mention different types of payments based on different metrics), but it's a method that can't be realistically done for every 3P AAA game due to the costs that'd involve. That's the compromise. Sony wants to provide access to every 3P AAA game for subscribers at the highest tier; their compromise is that the amount of time for that content is limited to at least 2 hour trails.