switches to (probably) T1 encoding at some point.
No. texinfo.tex has no concept of "font encoding". What it does (has
always done) is use the EC fonts for characters that do not exist in the
CM fonts, such as eth, thorn, quotesinglbase, etc. If those characters
are used in a document, then the fonts are needed. If not, not.
Gavin and others have made many changes to texinfo.tex since I stopped
being the principal maintainer, but looking at the current texinfo.tex
(2016-09-18.18) I think that is still true. -k