Regarding delays - for both 2.1 and 2.2 FD developers have said they were given extra time to make QoL and other improvements. So it's not like development of Season 2 got unexplainably longer - it was decision made by FD and it is most likely related on how they want to release Season 3. There's speculation that Season 3 is planned to be late because it will have all planned features from get go, in one big update. That's why FD stretches out Season 2 with more updates and improvements than they would usually able to deliver.
All speculation, but really, consoles aren't reason Season 2 is stretched out longer than we expected.
Well in a way this makes sense - one of FD's financial reports stated that pick up of Horizons was slower than forecast, although the base game was still selling well. It seemed to imply that a lot of people were waiting for season 2 to be functionally complete before buying it. Now, if a lot of people do that, it's diluting your revenue because by the time season 2 is finished, it will probably be discounted. If this is the pattern they are seeing, this may trigger them to develop "season 3" or whatever it's going to be called as a single big update and/or sell it in chunks with smaller prices.
Of course, the lack of season 3 could also be a sign that the game is going very well overall - if your old game and content is still selling well, it doesn't make sense to announce new paid content and encourage people to wait for the new content before buying in.
I'd not be so concerned about additional platforms consuming engineering time, but by the overhead of each platform's update QA and release process. Major feature parity across PC/XB1/PS4 is a given, but QA and certification is essentially subject to random events causing another (external) QA cycle for each platform, so the more platforms you have, the time (and effort by your release manager) to reach release readiness on all platforms increases, so you'll be tempted to relax the update cadence.
True. One other factor is to what extent it could consume non value add work a few years down the line when they are forced to provide backward compatibility with obsolete consoles. Let's say the game is still being developed in 6 years from now but for how long will they still need to support obsolete games consoles, at least with existing content up to a certain point in time? This could force compromises in game quality and a lot of backward compatibility testing.
On balance PS4 will be great for the game, but yes there are some risks and downsides as with everything.