[konikpolny]

r0lZ i think you could allow user to choose their own local font. I am using MPC-HC and if it can't find the font referenced it does substitute it with its own preferred font. I don't know about the other players. As regards font styles to mux i think it should be enough to enclose just the main one, but it should be tested. I also think that muxing font should be provided as an option.
The minimalistic approach you are suggesting is for a foolproof suitable-for-all players, and I understand that but it imposes its limitations and that is not necessarily good. I would vote for having the defaults which can be overwritten and advise about the consequences of the change.
I would prefer my own font but if you decide to only support arial, times and verdana it'll still be great. The ass is editable text format and the font can be changed in the sub file manually. It's also worth noting that for many players the ass subfile can be loaded externally and doesn't have to be muxed.
I'd also suggest starting with the most simple approach and allowing for more advanced support in the future.
Many thanks