Hopefully SM55/VXL gets back with you/Trey, they really would make a great addition to the hydratube lineup.
Regarding the question as to why more EVO owners haven't jumped on board yet, I can't answer for everyone, but I can give my opinion on it. Personally, I don't have a strong desire to own a hydratube. I found them to be far too expensive when I bought my EVO, so I just inverted into bubblers.
The way I use my EVO is not very conducive to hydratubes either. I mainly use my EVO sitting at my couch. The height is just right to have a bubbler sitting on a TV tray to hit. If I used a hydratube, I'd have to hold the EVO in my lap to hit it. Not a big deal, but not my personal preference either.
Another reason is resale value. A hydratube is a very niche market, compared with the glass world at large. I can buy a piece of glass with an 18mm female joint, and have no issues using it with my EVO. And if the time came to sell it, I'd have a much easier time unloading it.
One possible drawback of not using a hydratube is having to buy an adapter in order to use the VXNail. However, for ~$30-$40 you can get a nice adapter and have no issues using the VXNail.
All that being said, if I did ever decide I wanted a hydratube, there's no question I'd be getting one from Doughboy! However, the more likely scenario, is that I'd have him make me a piece with an 18mm female joint