re terminology: Studio equipment companies are (like many industries) full of commercial buzzwords. Everything between heaven and earth has been called "phat" and "analog", for instance

In the modular counter-culture, "snappy" has become a holy word which has caught on as its meaning gets dilluted. Wavetable synthesis probably sounded a lot cooler and selling to a marketeer than s+s, sample synthesis, and sampling. Another term that was used largely to obfuscate what the synth underneath really was about was "vector synthesis". In yamaha products, it's a combined fm synth and rudimentary sampler. In KORG (wavestation) it is actually a wavetable synth. Their common factor? A joystick for blending sounds and/or steering control messages with semi-alterable addressing.
Not to diminish the feature - It gave back a dimension of control synthesizers had abandoned since the minimoog generation. I think the distinction between a sampler and a wavetable synth being if the samples repeat after one cycle/period or not is very clear. Other distinctions (like if it is able to record a sample) aren't waterproof and have been blurred as new products have entered the market.
Quote:
I'm not sure if all this stuff would've made the chip expensive in the late 80s to early 90s though.
Most probably, that chip was already pretty advanced for its time. Today you can get pretty advanced synths/delays/reverbs on a chip, but they're also generally costly. Example of a
lower end FX chip. There might be bucket brigade chips on the cheap, but i don't know. The problem here is for a commercial, easy to source part, the legal dimension of emulating it can potentially get tricky (it's someone's product). For old stuff, you can't reliably source them. So i think there's two options: Emulate and program a suitable DSP pic / mcu / fpga, or make a circuit from more discrete parts (might be too expensive and labourous) and emulate that in turn. Or a combo/compromise.
Some FX are both cheap to build discrete, and easy to emulate. If you want do give each or some channels a suboctave side channel, all you basically need to use is optionally a comparator and essentially a d-flip flop. Especially if the sub channel is directly derived after tone generation (where the amplitude is known) and then summed/mixed in prior to any volume envelope (and filtering, if that applies). Mixing would require a programmable mixer, of course.
FM/AM synthesis is good in retro gaming (i think) because it offloads the CPU by some (but with 65816, would it matter?). Besides the audio range modulation, you can create vibrato and tremolo just the same way without continously feeding new pitch/volume data to the unit, and tremolo/vibrato would work independent of their famitracker-style instrument envelopes (apart from you wanting to change rate and amplitude of those effects).