This was my fear with Dolphin licensing as well. In the first few months it's VERY painful, but eventually the volume builds up. Also maintaining one-off payment option helps to maintain cashflow. For us it took 3 months to achieve 50/50 revenue from subscriptions vs one-off payments. That's with monthly license cost sitting at exactly 5% of one-off fee.

My gut feeling is that we'll see only a small number of subscription modules initially, only from long-term committed vendors. After a few months see more they'll feel the taste of stable growth and will start adding more offerings. In about 8-12 months I'd expect half of the market revenues to be processed as subscriptions.