I think the fact that we're getting a second Den-O movie probably means we will be getting a Kabuto movie - Kabuto overall was a slightly more consistant series that lends itself better to a movie, and was notably more popular. It'd be silly to make a Den-O one and not a Kabuto one.
No offense, but I think this may just be you as a Kabuto fan hoping for another movie. According to Igadevil, Den-O is pretty much the most popular series in the heisei so far. Yeah, Kabuto had slightly better ratings, but at this point in time I'm really starting to think that ratings don't really matter as much anymore. You couldn't really go anywhere in 2007 without seeing the Imagin plastered on some random stuff, and this happens every now and then with other series, but with Den-O it was done in
much higher numbers. Not to mention just how well the music for Den-O has done, look at the Wing form single, even months after Den-O ended, the single came in number 4 on the Japanese music charts.
Before Den-O Toei really needed a hit with Kamen Rider, the last three or so seres had pretty much failed to meet expectations, at least that's what I've heard. Den-O seemed to be a hit on all sides, high DVD sales, massive music and toy sales, its movie supposedly did better in the long run than any movie aside from Faiz, it had fans from not only the house moms and kids and Kamen Rider fans, but it brought in a whole new fanbase by using some of the most popular seiyuu out there. Heck, they even had that special stage show DVD and I'm at the point where I believe that a Den-O video game is coming, but actual hard work is being put into its creation.
If Toei wanted to make a new Kabuto movie, they would have done it by now.