As an aside, most companies for whom IE6 is an elephant-scale problem are using both AD and MS SCCM for user configuration management & group policy controls. CM makes it trivial to deploy stuff across the board, including complex software like OS service packs [and browser upgrades]. I posted before that my own org is in the process of upgrading everyone to IE8 right now, but we switched to Firefox as our standard browser about a year ago and are currently testing the new Chrome MSI (woohoo for GPO support), since even though Google's interpretation of the HTML5 standard includes a few things that aren't actually in the draft yet, it works much better with Google Apps.
You won't have to worry about IE6 in 2015.
Oh, and don't forget that a lot of proprietary corporate apps are written to work ONLY in IE6. I wonder if a "legacy" mode for new versions of IE would alleviate part of this problem. (And yeah, I know that there's a big fat bag of poisonous acid-spitting kitten-eating snakes that this would open up.)
The new auto-upgrade model Mozilla has adopted for FF 4.0 (and that Chrome has had for ages) makes upgrade cycles, for all practical purposes, negligible.
Chrome 6.0 was released on September 2. Since then, Chrome 5.0's market share has dropped to nearly 0%, with Chrome 6.0 picking up all of 5.0's share while also absorbing a good amount of IE's share.
If Microsoft instituted an auto-upgrade path for IE and released updates with more regularity, this would slowly become a thing of the past.
- You could do it as Chrome does and have a per-user install. I don't think Mozilla wants to do this.
- You could install a service or a scheduled task to do the work for you.
- MSI updates can be installed without admin rights if they're Authenticode signed, and Mozilla does have a valid Authenticode digital certificate.
I can't think of any alternatives to this problem. I am pretty sure I will still be considering IE6 while developing websites in 2015, let alone IE8.