Well, let me explain. If there ends up being two distinct systems. The points system for those that opt in to the new internal program, those weeks obtained from points users won't be available in II for those that opt to stay with the old system. So for those trying to trade in II, there will indeed be fewer weeks available, thus less inventory.
OK - if you are trading through II and a different exchange company gets the time (already possible) then the II inventory will be impacted negatively. But II already has no guaranteed access (it is the owners choice each year to deposit or not) and then they further reduce availability by giving preference to certain groups prior to general availability. So the average amount of available inventory may fall for II but it was never guaranteed, always optional and very hit and miss. If you depend on that for your trades it was never reliable and may become less so. One of the big advantages to any internal system will be the absolute availability of inventory (it is usually committed for XX years or even forever in any points based system) vs the hit and miss of weeks. That alone makes it far more reliable and easier to get exactly what you want than weeks/II can.