From the name and (extremely minimal) lede, it sounds like this page is making recommendations for all extensions. However, from the very first recommendation, it's clear that the intended scope is only extensions that are meant to be used generally, and especially those aiming for WMF deployment. This disconnect could lead readers to believe that an extension being developed exclusively for use on e.g. a single third-party wiki is either explicitly discouraged, or has to jump through unexpected hoops that implicitly discourage development of such extensions. I'm sure that such extensions shouldn't be encouraged, but I think it's a mistake to actually discourage their creation/use, explicitly or otherwise.
tl;dr This page's lede should be expanded to clarify what sorts of extensions it's intended for: all extensions, or only those intended for use outside of their originating communities/wikis. (Possibly individual recommendations should receive similar clarifications.)