One problem I have seen with autoinstall is that sequence of lines in install.conf is important.
It seems not to much to closes pattern. For example if you put 'Start ntpd(8) by default' and 'NTP server' (IIRC) in the beginning it would impact answers to questions having 'server' in the question. I don't have OpenBSD machine next to me right now, so I will post details later. One would also like to have a way to query all questions, right now one has to somehow guess or type them down, so they can be used in install.conf. It would be also nice if every installer would save questions and answers in install.conf-style file, so one could use it as template for later deployments. I'm looking forward for custom partitioning. Right now only solution is to build custom ramdisk and define own md_prep_disklabel() in install.md. My 2 cents. jirib