I am not a huge fan of Doc Rivers, but willing to give him a chance. D'Antoni is more of a Hail Mary play, smaller chance of great success, greater chance of total failure. The moment Doc was let go by the Clippers it was a pretty good bet Lue was going to head there. Donovan was my favorite, but he is long out of the running.
FO must be fixed to help the roster balance and construction. No coach will succeed without that. Rivers seems like he will have some effect there, which will at least push along some of the promised changes. Who the new FO folks and players will be can't really be evaluated yet, but we all know change is needed.
Larry Brown was a great coach with a short half life and terrible personnel impulses back in his time and got the Sixers to the finals.
Billy Cunningham was constantly derided as a know nothing X's and O's, good with players coach who couldn't win the big one, until he did.
The Clips were one of the teams that simply didn't adapt to life and play in the Bubble, maybe some of that is on Rivers, but a lot was just weirdness and circumstance. Rivers has coached some long gigs at his various stops and if the locker room got toxic near the end, that isn't unusual. Most coaches are not Pop or Jerry Sloan types that outlast generations of players with the same team, most have an expiration date where their voice has been heard too long and change is needed. If Rivers gives the Sixers 5-6 years of very solid coaching, has a good staff that complements him then he will do a very good job and the rest is up toe the FO and the roster they construct.
Changing coaches is only step one in this process (since the original step one of FO changes hasn't happened yet), but Rivers is as solid of a hire as you are going to get knowing the ownership group wants an experienced and proven coach, not an up and comer.