People have said the same about browser engines, that it's impossible to start and new one and catch up due to the unfathomable number of man hours invested. But it's happing, Ladybird browser is making incredible progress. With modern tools, the learnings from older engines and the lack of entering debt it's possible for a small team to build things on par or better than 30yo software.
I have no doubt that a small dedicated team could build a new parametric kernel and CAD package, particularly one that's open source.
There will be significant differences in demands made by the end users of a web browser and a viable CAD system for serious work though.
It is an extremely tough market that many have been shaken out of.
Reliability is a must, particularly on the data representation and exchange front. And those assurances carry ENORMOUS costs. Big money at immediate risk in downstream, physical product if that goes south at any time - spread across multiple manufacturers and other product lifecycle parties.
Lots of workstation compatibility certification work done on CAD kernels.
PLM alone, embedded in many engineering organizations, is a very sticky element for retaining a certain CAD program and certain kernels internally - and it is my understanding that PLM is where the major money is made (not so much on the per seat CAD licensing costs).
New grads are coming out from college today after using CAD company-supplied software in much of their classwork for 4 years.
Many CNC controllers use Parasolid internally for certain visualization and programming operations - machines that will be working on the floor for decades from today.
The fact is that the per seat licensing cost and lock-in tradeoff is simply not a serious issue for many - and such costs have become arguably marginal for even small design houses and manufacturers.
I have no doubt that a small dedicated team could build a new parametric kernel and CAD package, particularly one that's open source.