well, its not exactly the same principle.
The lo fi mod adds a new url for the low fi version, so it's not exactly as running a real table less template. It's a simplified version of the actual forum layout on another location.
SEO wise, it's not necessarily the best thing to do. You create a pseudo duplicate entry, two url with same content, but not the same exact code.
Both should show up in SERPs unless you do something about it, and this can create some confusion.
I usually prefer to concentrate all my effort on a single URL. The risk is to see both pages appearing in SERPs, at a lower position than if you'd only allowed one, and to see the lo-fi one a bit before the other one in most cases, which leads us to the second matter I do not particularly appreciate as a regular user : I do not like this much when I end up in a lo fi or printer friendly version of a web site when searching, just because these usually miss all the user friendly features the real web site has, and makes further browsing a bit less obvious IMHO. I'm not a printer
So it depends, accessibility is a real great thing, but I'm not sure we should always work on SEO all the possible format we run on a web site (printable, wap, lo fi and etc ...) as this creates as well some confusion, SEO and user wise.
I know many big web site do use and abuse these, but I'm not convinced this would be this great on the long run, at least, not in all cases.