I've thought about some of this recently, and while I don't regret being able to jump through the tech stack, or even do a sales call or set up a marketing funnel, there are definitely a few issues that come to mind.
1) If you jump tech stacks you're going to have to spend time getting to know the layout of the neighbourhood. Avoiding jumping across ecosystems will save you time in the long run.
2) You may never truly reach your full potential of really knowing a language if you're constantly jumping back and fourth between many.
3) Some employers will try to pigeonhole you and not take into account your broad array of knowledge (resulting in a lower offer). This may just mean that they're not the right people for you though.
4) Technology is constantly evolving, so you will become out-of-date with technologies you no longer use or use infrequently.
On the flip side:
* You can gain respect of your team and become a "go-to person" for helping them solve their array of issues. This can help give you leverage within a company (e.g. deciding to work part time)
* Having a broad skillset is perfect for starting a company if you are entrepreneurially minded.
* You'll gain mad problem solving skills.
If I were to offer one bit of advice:
Pick one tech stack and be a generalist within that tech stack - and don't let job listings dictate what you will spend your life working on / learning. Choose your work strategically.