First I don't have a solution, but maybe an FR that all midi gear need.
I looked at my daw, response time for REV2 is 3.7ms(179 samples/48k) where you have any reaction on audio when rendering it. It's up there with any midi gear, Nordlead about 250 samples, Hammond about that too, had some yamaha piano that took 370 samples.
So nothing abnormal with REV2 there.
Now to midi clock, which is 24 clocks each quarternote, so dependent on tempo what delays are in milliseconds.
Running at 100 bpm, there is a midi clock coming every 25ms. So just depending on phase of clock +/- 12 ms which is clearly audible. Plus response time of synth 4 ms.
We must remember midi is 31250 Hz serial if I remember correctly. 10 bits each midi event means 3125 midi events max every second on one port, about 3 events each ms. If you chain a lot of synths with midi thru and different midi channels with a flood of notes and midi CC these realtime events for midi clock will get delayed certain portion in there. These are built in limitations. I think one NRPN is 4 bytes and over 1 ms each.
So design midi gear setup accordingly thinking about this. Doing it one way midi clock will be fine, and another way it can lag enough to hear it.
So internally I think all midi gear should have an offset setting for external sync for this reason.
- I think this is all that is needed if Sequential would look at it
On 2019 first time I looked at REV2 I already saw a report on lag on external sync. I bought mine just last year though. I am not dependent on external clock so far, but I understand many are depending on it.