I doubt it. The B-2 was cut because the cold war ended and because it was absurdly expensive to maintain thanks to its 1980s stealth tech. The radar-absorbent material used for the B-2 degraded very quickly and it's a large aircraft, so that means absolutely constant work to keep it functioning as intended. The B-2s are based out of Missouri and when they go on a mission they fly all the way to the other side of the wold and then back to the central USA. Why? Because Whiteman Airforce base is the only one which has the massive climate-controlled hangars you need to stick the B-2s in to keep them from falling apart while on the ground. If the US built a fleet of 100+ B-2s in the 1990s we'd have ended up with a fleet of cutting edge bombers which cost more than $100,000 per flight-hour to operate and no one to use them against. A fleet of 100+ B-2s during the 2000s would have been a massive white elephant.

The B-21 is different in two important ways.

First, the B-21s stealth tech is derived from lessons learned from the F-35 program. The F-35 is a tactical fighter which the US and most of its allies are buying in very large numbers. They need to be stationed just about anywhere and can't require ridiculous maintenance to keep their skin from falling off. That would be impractical for a large fleet of aircraft. As such, a lot of work went into making the radar absorbent material used on the F-35 dramatically more durable. The B-21 gets to piggyback off of that and as a result it will be much more feasible to actually have a large fleet of them.

Second, there's a new cold war heating up with China. Anyone whose ever looked at the Pacific ocean might notice that it's kind of large. This makes range a major concern for combat aircraft. A medium stealth bomber with extreme range is essentially perfect for this environment because it can reach anywhere and is very hard to actually find once in flight. If you are a surface warship force, being hunted by a bunch of nearly undetectable aircraft which can be anywhere at anytime and can each carry more than a dozen large anti-ship missiles is going keep you up at night. The B-21 will likely end up being a very important piece in the US naval strategy in the pacific.

I wouldn't be surprised to see significantly more than 100 get built.

Possibly, or possibly it will follow the same pattern as the F-22 / F-35 where the aircraft that was the true breakthrough (F-22) was expensive and had production slashed but the "cost optimized" version (F-35) is now being produced in large numbers [1].

1. I'm aware the F-35 development program itself was a boondoggle, but there are still building a ton of them right now.