Note this has been discussed before. The biggest problem is that calling potentially slow and expensive API modules from the page parse is probably not a good idea.

(In reply to comment #1)

Note this has been discussed before. The biggest problem is that calling
potentially slow and expensive API modules from the page parse is probably
not
a good idea.

Won't it be counted in Lua execution limit?

Note, some api modules are not safe to call during parsing, since the invoke $wgParser. (Most notably action=parse and action=edit. however we probably wouldn't want to allow those two anyway, but there may be other modules that do this)