.mobi css to desktop - the reverse situation

For those with established .mobi’s, is there anything really stopping the adaptation of these for desktop display?

Creating the css along with the handheld detect, there are two main things I can think of:

a) the issue of character count. Possibly that rankings could be hard to get with such economical text counts. If a conditional statement/css places added text, would this nix Google indexing despite the separate platforms?

b) the long term viability of the extension. Will it be around in 5-10 years?

I don’t think the extension is a deterrent in itself for getting traffic for “typical” results.