While the Chelton Gadahrs does have a WAAS GPS, it a term being very loosely used these days among products. The WAAS GPS it has does not qualify it to be used for Lnav/Vnav and LPV approaches. To date, the only systems that are approved are the GNS480/530W/430W/1000, and a FreeFlight GPS. Chelton has said that they will also be releasing a full LPV capable remote-mount GPS (last I heard it was late this year but you know how those things go). You need to look at the EFIS for what the EFIS features are, and realize the WAAS GPS (for REAL Lnav/Vnav/LPV capability) is an add-on to any of the EFIS's except the G1000...and even the G1000 only has it from what I understand because it's actually built using the same components from the above listed. (A G1000 incorporates special 530 type radios and things internally)
So for people comparing EFIS's, your LPV capabilities really rely on one of those above systems to be tied in somehow. Even when GRT comes out with their "WAAS" GPS, it's not intended to be on par with the requirements of the actual honest certified GPS's listed above, from what I've heard. So the thing you see as a limitation is a limitation for all of the systems...which is why you see so many 430W's and 480's in the same panel. Now, wait a short time more and when a remote mount WAAS GPS box can be added that honestly makes the system 100% capable of any GPS approach, then it will be the ideal situation. The nice part is, you can fly behind it for a long long time gaining the proficiency you should really have, and add that box when you want to throw the added $$ towards it.
As far as ADS-B goes, yes, the Chelton is ADS-B capable. Remember that Chelton was actually THE system that was put together for the Capstone project to test the feasibility of ADS-B in Alaska, so it was really the same thing I'm flying today that it was done on. As I haven't pursued ADS-B yet as an add-on to mine, I can't tell you if there is any revision difference in the GDL-90, but from what I've heard it was indeed a GDL-90 of some flavor that was used for ADS-B. That question would be a good one to call Chelton directly about. In the configuration pages of the system when you set up Traffic (or maybe it was weather) though, you have choices of things like Ryan TCAD, real TCAS systems (the GTX330 uses a TCAS config), or ADS-B. So the systems indeed have the configuration available. All you need is to find the box and buy it. I'm waiting a little while to see when ADS-B gets more reasonable yet, as my GTX330 has now already given me coming up on 2 good years of TIS for a lot lower cost. It's going away they say, but it is a VERY slow departure.
If you ever want to swing up this way you're welcome to go for a flight.