I think that it's a bit unrealistic to expect such a development for the G 70; if you ask me why, I will answer that the Fantom X already comes with an internal sampler, and this makes all the difference in the world, when it comes to audio recording.
In the second place, I have a feeling that the G 70 is more or less complete the way it already is, and Roland made the mistake of limiting it too much.
I too would like a sampler, and more expansion slots (instead of just one), and also master keyboard functions (which means the ability of sending bank and program changes to external sound modules and storing them into registrations).
Well, my feeling is that, if one is looking for all these features, must also look to other keyboards, like the Motif ES, the Fantom X or, speaking of arrangers, the Korg PA 1 X pro.
Sad but true.
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Korg Kronos 61 and PA3X-Pro76, Roland G-70, BK7-m and Integra 7, Casio PX-5S, Fender Stratocaster with Fralin pickups, Fender Stratocaster with Kinman pickups, vintage Gibson SG standard.