Trent, to get a meaningful answer - even as a bit of speculation by the poster - there needs to be background numbers to support what percentage of hobbyists has even converted to DCC so far. Although DCC may be at the forefront in the magazines, I've seen nothing based on actual surveys that suggests that DCC acounts for even half the hobby currently. Lacking that necessary information, your question simply becomes a matter of picking some random number out of a hat.
What also needs serious consideration is the fact that a very large segment of older hobbyists with large and established DC layouts are not particularly enthusiastic about going back, re-wire everything and otherwise rebuilding the power grid on their pikes for DCC. It's likely that the majority of these will never convert.
There was a brief push in the very early 2000's for manufacturers to go to all DCC engines that failed, but more recently "stealth", or DC-only, locomotives have again become rather available, along with their DCC-ready counterparts, as the manufacturers realized that they were missing a large segment of the customer base that was strictly DC.
So, I'd say that until the current generation of senior hobbyists are gone, I don't expect DCC to truly take over the hobby, justifying my 9+ years vote.
NYW&B