You could probably do away with several chassis members and still be tough enough for just about any game in the Bumper Era
We have used T-slot extrusion (Bosch 20mm rather than 80/20 because we can get it at cost) for our frames since 2005 and they have served us well - only in 2010 with the vigors of bump crossing (and some weight problems resulting in fewer cross members than we would have liked) have we had any structural problems.
We have learned a few things about these types of frames through the years:
1. Through-bolt wherever possible. At the very least, leave it as an option. Remember that a 3-way joint is impossible to through-bolt when it's in the middle of a frame member (like on the front of this design).
2. If your extrusion manufacturer offers multiple types of "corner cube" connectors, go with the beefiest one you can get. Direct impacts have shattered our corner cubes in the past.
3. If we are going to use T-slot connectors on a particular piece, we prefer to use slide-in (not drop-in) T-nuts for the strongest connection. To facilitate easier insertion, we often mill the T slot wider somewhere near an end to provide an insertion point.
4. Think long and hard about using the T-slots for holding your pillow blocks. While having a sliding axle makes tensioning a chain trivial, locking it down in place requires that you diligently tighten everything after EACH match. Using a cam bolt or turnbuckle to make sure your pillow blocks don't slide can be a good idea if you can figure out how to do it in a lightweight way (usually we just through-bolt and add idlers for tension if necessary).
I can tell you that the design just as you have it will make for a rock-solid frame that will serve you well! Good job.