That's not a revive though, revive (at least to me) implies it's dead.

> The spice core that ngspice is built off is terrible code. It has a long history going back to 1970s era fortran. Starting fresh is probably preferable

That code is also hyper-optimized for performance. I sincerely doubt you are going to match the performance easily with any random rewrite.

Now, if you had a very clear idea of why the code was making assumptions from the 1990s that are no longer valid, then you might stand a chance of producing something that would outperform it. Or, perhaps, if you had particular knowledge of modern high-performance numerical libraries that you could apply to the problem, then you might be able to beat it.

However, circuit simulation is remarkably difficult to get right (stiff systems with multiple time constants are not uncommon) and generally resistant to parallelization (each device can have its own model which are a unique set of linear differential equations).

If, however, the legacy of ngspice bugs you that much, go look at Xyce and see if that is more to your taste.