The concept is good, but the proposed implementation is not.
Sequential release numbering implies eventual replacement, or at the very least dropping of support. A commitment to continue developing MJ8 ("the music-only product") is somewhat hollow, because someday your financials will dictate a new, full release of the "music-only product". What then? Will it be called MJ10, and then the follow-on to MJ9 ("the full product") will be MJ11? HP got themselves into this mess a while back with HP-UX. Even-numbered releases ended up being for Unix workstations, and odd-numbered releases for server hardware. It was silly and very confusing. If you do not plan a future full release of the "music-only product", then the direction that has been so thoroughly discussed on this forum is simply being delayed.
I honestly feel that the video, DVD, TV, etc. functions of "the full product" should be offered as a plug-in to the "music-only product". If that marketing angle makes you wince, then reverse it. The default purchase is for "the full product" for $40. The purchaser has the right to check a box declining the video, DVD, TV, etc. functions, in which case he gets the "music-only product" for $25--if he decides to purchase that capability later, it costs him $20. The pricing is the same as your model, but the product will have consistent release numbering.
It's all in the naming. Offering MJ8 and MJ9 simultaneously implies MJ8 will be discontinued or unsupported someday.
Scronch