It's not an issue as long as you use a mainstream language, but using a language or framework that will be perceived as a dead end can hurt your chances to hire and retain people. If you're a large or prestigious enough employer you can probably compensate that as long as you're willing to train people.

Programming language alone should almost never be a big enough issue to force a rewrite, but if you already have serious other issues that force huge changes you might as well look at it at the same time.