Rev L - needed for a small layout?

I have a small Fastrack layout and added a DCS used TIU a year or two ago and run it in passive mode with no issues. I do get an occasional signal loss but I think that is more of me not keeping the track clean as much as I should. So, I think you should be fine and older TIU's can be had for a pretty good price.

As far as running a PS1 with a PS2/3 engine it would be a lot like running a conventional engine with TMCC/Legacy since it can be done but enough voltage needs to be present to run the command electronics.

The big Rev. L changes are under the hood. The Rev. L is much improved over previous models.

I would strongly recommend that you purchase a Rev. L and that you avoid purchasing a used TIU, especially from eBay.

Let me rephrase my question this way: Is a non Rev L DCS system worth upgrading to from conventional control or should I just wait until MTH eventually comes out with their wifi module and iOS app which is how I ultimately want to control my layout? Switching my N scale layout to DCC has given me the itch to switch my O gauge layout to DCS but maybe it's not worth it even as an interim step? 

Even if I could find a Rev L system in stock I'd have a hard time justifying the price of the remote knowing that MTH is working on a wifi module and iOS app. Working in the tech field I have a really hard time justifying spending $200 on a remote which is only capable of running toy trains and nothing else. For that same money I can buy an iPad or Android tablet that is capable of vastly more. 

ANy DCS is better than none.  Remotes have not changed.  Barry's advice about not buying used from e-bay is good advice.  I have a large layout, with 2 original issue Rev Gs and a Rev H.  No problems.

If you're buying new, spend the money for a Rev L.

Is a non Rev L DCS system worth upgrading to from conventional control or should I just wait until MTH eventually comes out with their wifi module and iOS app which is how I ultimately want to control my layout?

No matter wether using the app or a DCS Remote, you still need a TIU. The WiFi module will be ann add-on to a TIU, not a replacement for one.

SeattleSUP,

   IMO when purchasing any of the DCS equipment you want to purchase the latest revision, and never purchase from anyone but an autherized MTH dealer, you want the replacement guarantee that comes with the product.  The only other way to pick up the DCS equipment is from one of the MTH certified Tech here on the OGR, they will supply you with good equipment at a reasonable cost. 

PCRR/Dave