Just had an interesting idea and I thought I'll see what everyone else thinks about it:
Wouldn't it be nice if in multi-domain environment you could mark one of the domains as "admin domain" so that all users accessing their admin area used that domain? Kind of similar to "domain used for the administration area" functionality of the Domain Mapping plugin.
The reason for this is that it is quite common for shared hosting to only support one SSL certificate per account. So, if you use Multi-domain on such shared hosting then you can't restrict access to your admin area to https only.
What do the rest of you think?