This really does line Josh up to be next-in-line for a couple of reasons:
1. The team made a "commitment" to him, which sounds like they are going to pay him to wait.
2. He said he was concerned about uprooting his family, but he's still going to have his kids over the next few years so that concern will last longer than BB will be around, and
3. I don't think another team will seriously give him a shot to be their HC after watching him string along two teams the past few off-seasons.
The Colts are screwed now, having let all the other top candidates sign elsewhere. And all those new coaches have hired all the top assistants too so even if they could get a top-notch coach, he would be at a serious disadvantage to begin with.
So I don't think another team is going to let him do that to them. They will not take him seriously, seeing how deep his roots are in New England. Josh probably knew that if he turned down the Colts, he'd have very few options in the future, and must have had some type of assurance from Robert AND Jonathan since we don't know when Robert will go.
Putting it all together and I think Josh will wait now, and if BB was serious about not coaching into his 70s, puts that at around 5 years and ticking.