> The LaTeX team have recently taken steps to extend the LaTeX2e kernel to
> provide some low-level support for post-TeX90 engines.

This sounds a little funny ("we recently added support for post-90
things"), but thanks!

> We are looking for feedback in two areas. Firstly, does the
> functionality provided cover the needs of package authors using LuaTeX?

The whatsit allocation is still missing, maybe it could be added to
lualatexsupport?

> Secondly, we would like input on how a transition to new support code
> can be managed. We are reluctant to suggest a complex compatibility
> layer for either our code or the existing packages, and suspect at this
> stage that a clean 'step change' may be needed for packages working with
> LuaTeX. However, this is a complex area and needs careful consideration.

To be perfectly honest, what I'd like most is a pull request on the
luatexbase repository... Maybe luatexbase could detect if the new format
is loaded and just skip all the features already provided? This includes
everything but

https://github.com/lualatex/luatexbase/blob/master/luatexbase-modutils.dtx

(and whatsit allocation, but I hope it can be in the format).

Thank you,
-- 
Elie