Frank,
The author, Valloric, is a graduate student who is shoehorning Sigil into his graduate work. From what I understand his priorities are squashing bugs in this program which is still in beta, quickly implementing features which are easy to do and finally working on majorly needed features. All this with a backdrop of having to depend on underlying software written by others which is changed on him causing failures or performance issues in Sigil.
If there is a feature which is desired or something which needs fixing, posting it to the tracker,
http://code.google.com/p/sigil/issues/list, keeps it where it has his attention.