All being equal, it's better to have a team writing code that is useful to the system or project or whatever ASAP.
If an individual insists on prototyping in a language that nobody else can use, then they should either carry that prototype into the team's ecosystem, or start prototyping in that ecosystem and learn to be productive that way.
If option A, let's hope that "write twice" is fast enough that they are productive. If option B, they may take a productivity hit but will probably catch up.
The third option of "I'll do lisp you do <teams ecosystem>" is not very pro-social. Come integration and debugging and maintenance time, that Lisp-er is not in a position to help. That's an undue burden in the rest of the team.
I can't count the number of times someone published their open source project and inevitably people in the comments started questioning their language choices, because they wouldn't be able to use it in their "team", and how that choice is ultimately harmful for "the community". Now, you're not doing that exact thing here. I'm just thinking about how all that focus on "the team" and "the community" often goes too far.
Personally, I'm not going to do anything in Common Lisp, but I'm always happy seeing other people doing their projects in that language (and many others).
That's fair.
> I can't count the number of times someone published their open source project and inevitably people in the comments started questioning their language choices, because they wouldn't be able to use it in their "team", and how that choice is ultimately harmful for "the community".
Yep - not paying means not entitled to anything. I agree there.