I'll join the speculation game as well. I think that Marriott owners will only have access to the following:
1. VSN Flex Pool Units (8 Months or Less) - This may be the reason why Vistana/Marriott over the recent years were so aggressive with pricing as long as you traded in a deeded week. If I remember correctly; in 2013 one needed to spend upwards for 20K of new money to bring a resale unit into VSN, then it dropped to 15K and most recently 10K. This in IMHO was designed to increase this pool.
2 . Non Flex Units that convert to DP - This allows the Flex Pool to be dynamic. This also allows customers to have a more "try and buy" feeling about DP Network. If they like it they can permanently convert their deeded units through the purchase in the DP network and now those units reside in the Flex Pool. This will now allow the converted Vistana/Marriott owner to access Vistana Flex Pool 12 Months out.
I do think the DP network and VSN network will remain in place but the cross conversion will give owners the appearance of more options. As far as deed weeks are concerned I feel those individuals that are able to book at the 12 month period will not have to worry about competition with Marriott owners since they will more than likely be limited to 8 Months or less. And those Vistana/Marriott owners that do purchase will only be able to pull from the Flex pool of units. I also feel that mandatory units (used for points only) may become less valuable in the future if more units are moved to the Flex pool (via conversion or Marriott manipulation).
In the end deeded weeks where one wants to vacation may became the best option in either network. Once again this is just my opinion. I'm just joining in the speculation game