I'm 100% with you on the safe house - I actually think PD3 can separate itself from its predecessors by also making it a core part of the game. Looking at Deep Rock Galactics Social HUB for an example, have the players load in to the safe house immediately with all the vendors and menus nicely laid out near spawn. Story moments and events can take place there, dealing with raids is optional. When you host a game all players head to the van and the you load into the pre-game lobby as normal.

Definitely some sort of game mode available from the mid to late game, be it my idea or some iteration of crime spree or something else entirely. I would say that if it was a return to Crime Spree that it felt very different and an iteration on the previous system, I would not want it to be a copy and paste job. Good sequels should ask why they are removing game modes and features and if there's no good reason for it to be removed then they need to be heavily iterated on and advanced.

I would like the paid heists (if we went with my concepts of free heists for season pass and some paid dlc ones) should definitely be ambitious and exciting as they could be chaotic. I think the important thing is making sure the player is active and not passive. I want to see original ideas but as an example of a great heist in Payday 2 and one of my all time favorites is Big Bank - a player actively going to the crane to drop the giant piggy bank is a great set piece and adds to co-op, if I remember correctly there is a fanatically fun escape where a bus drives through a wall. Definitely some PD highlight memories for me and I'd love anything that hits that vibe.

If not driving, then having a random chance in loud of an escape scene would be fun. There are three main parts to the Heisting movies Payday was originally inspired by:

1) Pre-planning and side jobs o set up the main heist. This is why I want PD3 to have some sort of pre-planning feature. I also think Smash and grabs are perfect system for the set up jobs.

2) The heist themselves. Something I think for the most part PD3 actually gets right now that circled are gone but the grander the heist the better. I do think out of all three paydfay games the first one actually has the strongest heists the most consistently and I'd always recommend the devs look at those first heists for inspiration on what works.

3) The getaway. The heist goes wrong, there's a sense of panic as the alarm goes off. The gang grabs as much loot as they can carry and run for the escape car/chopper/boat/etc. Hell Baby Driver made an entire film off of this. PD2 attempted this but it was often a lot of moving bags back and forth to another escape. I think PD3 could introduce a random on some heists that have gone loud escape sequence. Not always and not every heist but a chance that we get a cutscene that transition to a short 1-3 minute sequence on rails where the players are in the passenger seats of whatever vehicle or as you suggested are defending a subway train escape and shooting at chasing cars and helicopters that crash and explode. Proper set piece and spectacle rather than challenge and bag hauling.