[didibus]

Talent retention is needed tp be considered also. Engineers do want opportinitues to learn new things and experiment. If you're too draconian you might see top engineers leaving or moral being low with discontent engineers who might in turn be less productive.

[cobbzilla]

There are always interesting problems to solve and new technologies and solutions to use. That fun definitely never ends. But a whole new language (not counting small glue/config languages/json dialects/etc), a new source base for the team, one must be cautious (and they always start small, more temptingly). It's a potentially huge and maybe not great investment being pitched. Do your due diligence.