Artemiy:
The ESQ1, which used digital waveforms that were burned onto a chip. It had oscillator sync. I don't know whether they had some way to do that using an analog circuit, but it definitely had it. And this was back in 1986, long before computers were fast and cheap enough to handle it using analog modelling. So, it
can be done without algorithmic processing -- it just might take something that Roland is unwilling to implement on their products, citing its expense.
And it
could be expensive. The ESQ1 also had 8 Curtis analog filters -- something that, by today's standards, is a luxury.
- Sammy
P.S. And you are close in your assessment with respect to the Kurzweil synths. They actually use DSP algorithmic processing to get hard sync, along with every other synth "effect" that they can accomplish. This includes all filters. I do know about this -- I worked at their R&D plant in Waltham for about two and a half years.

Yes we did.