Let's hope Starship lift capacity will make Webb obsolete in a decade!
Granted a lot of that was scope creep but nonetheless, I'm betting it's not launch capacity that's the bottleneck.
Whatever follows probably won't be a big telescope. It'll be all the little experiments that couldn't find funding over those 30 years because there was nothing to launch them without breaking the budget. There's a lot of progress deferred because every launch had to be big.
It will be another infrared telescope. Hubble's capabilities have been all but surpassed by ground-based optics. Some of the new giant telescopes already being built will easily surpass Hubble (100+foot mirrors etc). What JWST does is see in infrared, something that ground-based telescopes can never do as IR is absorbed by atmosphere. So whatever replaces JWST will likely be another, bigger, IR telescope.
https://www.tmt.org/page/about
>>With its 30m diameter prime-mirror, TMT will be three times as wide, with nine times more area, than the largest currently existing visible-light telescope in the world. This will provide an unparalleled resolution, with TMT images more than 12 times sharper than those from the Hubble Space Telescope.