Some way of applying a global filter Would be great - not sure about the different login implementation, mind.

This possibility of keeping clearly apart "work" and "home" is essential to me. I just do not want to remember some things about work when I am on holidays. I would imagine something as a "context" switch. Everything (tasks, labels, list) could be associated with one of those context, and *nothing* about the "home" context would appear in the "work" context and the other way around.

A couple of options
1) To have JOB or PERS in the begining of list - that helps to sort out tasks.
2) I have dummy locations for Job and home tasks - that helps me to identify the place (sometimes i need to do smth in job location but not related with job)

Several smart lists helps to identify of the task is personal and where it may be done.

I'm only a recent user, but I've found that using work/home lists in conjunction with smart lists can effectively create this boundary. To save time, you'd need to create tasks at work while in the work list, so that you don't need to manually add that metadata. I'd prefer, however, to have separate accounts.

Completely independent areas would be great. I've found massaging the existing functionality tends to lead to overly complex Smart Lists as I try to include stuff I do want to see vs not. I want to be able to use multiple lists for both home and work.
At the end of the day, I'm trying to avoid buying RTM Pro twice, however I may be receptive to paying a small addition for a second account.

I think smart lists and tags accomplish this pretty darn effectively. I have a list that checks if tasks are untagged, or erroneously tagged with both work and home tags, and then the other lists keep everything sorted automagically.

I agree with selyaev.alec and ranbarton. Lists, Smart Lists, tags, and locations all provide a very good way of doing this.