With much cheaper & increasing competition from China in triplets like SW Esprits, the 4 inch market was/is relatively saturated. Tak cater for imaging with their FSQ85 & 106 quadruplets.
It could be TSA120 is next to go. But that IMO depends on if a 125DZ doublet follows. Imagers have the TOA130 & 150, but have lost the FSQ130.
Vixen now only run up to a 115mm doublet and 100 tripet, Borg 107. Takahashi therefore have their home market in 120mm+ refractors to themselves? The TSA120 covers both visual and imaging, excelling in the former, but with own brand competition in the latter. A 120 fluorite doublet would sell, but maybe as one would be new, with the existing competition, would it hold up against the rest?
I can see light weight would be an asset. It may use a FC100 or TSA120 tube, 2.7" focuser, DL clamshell. So only the lenses and cel would be new parts.