Hello! I have thought of this design.
If you put the camera and focuser in the tube itself, the mirror has to be VERY large in order to handle the filter wheel that would handle a full frame sensor. A 20" to 22" primary mirror can just get the central obstruction to 40% with most filter wheels that can handle 2" filters needed for full frame coverage.
Even coming off the secondary mirror to a traditional Newtonian focuser, the secondary mirror has to be about 40% obstruction to make it worthwhile - see Takahashi Epsilon HD for an example. Mel Bartel's site suggests such large obstruction for reasonable illumination of the focal plane. The larger the primary, of course, the small the secondary - but even then, getting to 33% central obstruction and good illumination requires a primary of at least 18"
The problem becomes engineering an appropriate secondary holder that can handle the weight of camera and focuser should you choose to go the route of having the camera and focuser at the traditional site of the Newtonian secondary mirror. It has be be really beefy, but designed so that vibrations do not set up a resonance that would kill any astrophotos. The big Ritchey-Chretians can give an idea of what those manufacturers had to do with their secondary holders in order to make sure they are stable. This had me very concerned since it would be a one off design for me, and I usually mess things up the first time I do them!
If you plan to use a full frame DSLR or a one-shot color cooled camera at the position of the secondary, why not consider the Celestron Rowe-Ackerman or Celestron EdgeHD? Both cover a full frame. The former would have to be used with a DSLR or one shot color camera (like QHY600) at f2, the latter at f10 (of f7 with a full frame focal reducer). The engineering mechanical details have been worked out and they are plug and play. The 11" Rower Ackerman is fairly reasonable (the 14" is much higher priced!). The 14" EdgeHD is fairly reasonably priced as well. Of course, as has been stated in the past, the scope is just the first step - the mount becomes the limiting factor.
If you wanted to stay wit a smaller frame camera, say with a diagonal of 20-22mm, perhaps a Night Owl 0.4 focal reducer on a traditional SCT giving f4? or Optec Lepus focal reducer on Meade f8 ACF giving f5? Those combinations would be match fairly well according to their literature.
Additionally, you could try a slumped mirror design - significant weight savings. For a 10" primary mirror, you could use an aluminum tube or phenolic tube whether you do a slumped mirror or traditional thickness mirror. And, with a traditional secondary mirror, it would get you up and running fairly quickly. If you then decided to try the camera and focuser inside the tube, the focuser and coma corrector would not need to be changed, just repositioned once you assure yourself of a good secondary holder and tube for them.
In summary, it comes down to the type of astrophotos you want to make. OSC or filter wheel? Full frame or smaller? Astrophotos for beauty or science (? photometry) or both. Finally, how much can you experiment with a design - does it have to work the first time (cost constraints?) or can you experiment, sometimes over several iterations and over possibly an extended length of time to get the design right? Best regards.