I've frequented their blog everyday, mostly cause they usually have some nice vore sketches there. But I don't really translate the text, otherwise I feel I'd be wasting my time for the most part. But if there's anything I can go by with their concept pictures through out the last few months, it seems like their next project will possibly be another Card Quest game. And with how the last picture is in their post from today,
http://dgallon.blog75.fc2.com/blog-entry-3459.html, I'm taking a guess that it'll be inspired by the Dragon Quest games.
As for a sequel for Echidna Wars, I don't really know. They use the characters from that game a lot in their sketches, but that's pretty much all I've seen relating to that game on their blog for a while. At least picture wise. Not to mention that this game wasn't even really a sequel to Milia Wars. More of a remake and extension. Also, I think they have to get in touch with ASIMOFU, as I believe they did the sprite work for it. But they only really post on their Twitter, which is more text.
Anyway, long story short, I think D-gate's next project is another Card Quest game. I just hope it's not gonna be another 5 years before we see anything relating to another Echidna Wars game.
When it comes to most bosses, thank god for obvious, glowing weak spots.