If I'd joined under the blended system way back when, I would've gotten out when my ADSO was up.
It's not so much the value of the TSP you can walk away with. Let's be honest, the 4% federal match (of base pay) to TSP under the new system is a negligible sum. Even an officer who serves 10 years is only going to have on the order of $25-30K of matching contributions over that time. It's a whopping $2-3,000 per year.
The 20% reduction in the pension is a much bigger deal. If you assess the cash value of the pension by getting an approximately equal inflation indexed SPIA, it's a loss of $200-300,000.
Which of course is why the military is doing it. The new system is a good deal for the military, not servicemembers. No matter how they dress it up, its net effect is to dramatically reduce pension costs for lifers under the cover of tossing a couple bucks at short timers. They even try to hose the lifers one last time with the lump sum / reduced pension option at retirement.
Of course fewer people will stay until retirement ... whether medical corps or not. The BRS is clearly, objectively, a dramatically worse deal for lifers.
If you're 18 and joining for the GI Bill it's great, though. They'll get out as an E3 or E4 after 4 years or so, and have a couple thousand dollars in matching contributions. Assuming they opted into TSP contributions in the first place ... which most probably won't. Teenagers need beer money, er, I mean, non-alcoholic beverage money, not retirement savings. And so the military wins again - odds are that a majority of the people who'd benefit from the new program won't even opt into it in the first place.
As a cost saving strategy, the whole thing is brilliant.