mm_flynn,
I was initially responding to chevvron's rather sweeping...
'What's the latest on Mode S'?
It's an unnecessary waste of money as only a very few ATC units can make use of the extra information.(LARS units the ones who need it most - generally don't have the necessary software)
Then tried to answer your question during which I did say you may consider Mode S may not be entirely relevant to you.
That said, I think it should be stressed that even if not directly relevant to you it does make for an overall safer system. That may or may not in itself be of a measurable value to you or anyone else here.
I suppose there's also the spectre of mandatory transponders still on a distant horizon. I'm no technical expert on the subject but I believe if we ever get to a position where pretty much everything is carrying a transponder then the bulk of them will have to be Mode S for radar processor info overload reasons (though I stand to be corrected if that's not the case).
Also, to the best of my knowledge, a Mode S transponder is a Mode S transponder. ELS and EHS are basically just terms that someone has made up to indicate whether or not anything extra by way of DAPs is being downlinked back to the ground from a suitable source in the aircraft via the Mode S datalink.
I look forward to future discussions* about why GA is having to buy yet more boxes because the ATC system is shifting towards ADS-B or some other type of 'progress'. You just can win, can you
* Actually I don't because I'm reasonably confident I'll be retired by then!