To summarise, everyone appears to be in furious agreement :)
Now 0.21 is out, Matthew, whats the oldest version where all the things used in the current Geany are supported, 2.16 or 2.18.
And can you and Nick test with windows to decide which version we package with Geany. I don't have a full list of what is wrong on windows but some things that have been reported as wrong like drag and drop are currently irrelevant to Geany and some like themes are not essential.
Newer versions to support big new ideas can be discussed separately from there :)
Cheers Lex