PIC16 doesn't have nested interrupts. Theoretically, you can do it in software, but it is so inefficient that it certainly isn't worth it.
If some of your ISR are very long, you can put periodic checks in them at convenient locations to check flag and have them CALL other ISRs. This doesn't result in an instant response, so adds some variable delay. And it only works if you are careful to identify and sort out any memory conflicts. The memory conflicts are not necessarily overwhelming. It depends on what the ISR's are doing. They might be completely unrelated and/or use not much memory. This would be unusual situation perhaps, and you won't get nanosecond latency, of course. Unless you were doing this check/poll at super high speed in a "dead delay" such as waiting for ADC pin to stabilize(Leave it to imagination why you would be doing this in an ISR, but I've done ADC read in ISR, yeah).
I normally write my ISR as series of subroutines called by the main ISR in series, anyway. If one were to be called by other ISR, it is self-contained. If/when it gets called again in the main ISR, it will be serviced, already, and the ISR will move on to the next in line, down the checklist.
Unless you have a single interrupt in any given priority level, first thing ISR has to do is check if it is enabled and triggered, anyhow. Theoretical minimum latency based on hardware is only going to be achievable in this scenario. Using PIC with single interrupt priority level this is a rare luxury.
Back to topic, though: I think EE's and hobbyists have more varied interest than just ballistic missile guidance systems. I agree to some extent that as you work with more complex device and tools, it rarely makes sense to go back to more basic strategy/tools. If you can do the job with 100x more memory and transistors and multiple layers of software, why "relearn" how to do it more directly? You have worked so hard to learn the "best" way to do things with the complex tools and devices. But when you mention bugs which take years to sort, maybe it's partly because you are relying on all these layers for too many things... We landed people on the moon without 32 bit microprocessors and fancy compilers.