>  I suggested LaTeX should have a PlainTeX class, so that could
> conveniently migrate from PlainTeX to LaTeX...

I find

latex &plain  file.tex

usually works quite well.

You can also go
\documentclass{article}
\usepackage{plain}
\begin{document}
\begin{plain}
\input{file}
\end{plain}
\end{document}

which works most of the time as well. But probably not for the kind of
article that appears in TUGBOAT. It is not too hard to write a TeX
document that really excercises the obscure bits of whatever format it
is aimed at, and so really will not run on any `emulation'.

David