I keep hearing that the "selling support for FLOSS" business model is extremely hard to keep profitable, with Redhat always the honourable exception to the rule. It makes me wonder whether a distribution could make its money by cutting its distribution costs to the minimum possible - ruthlessly sticking to unpatched upstream for example - and instead offering customers a more-or-less guaranteed bug fixing service on all software across the distribution. Fixing bugs for a fee is probably too expensive for a small customer, but if an enterprise-size customer notices that a particular bug is affecting the productivity of a lot of employees it would probably be a good investment for them - and if a bug was causing problems for several customers the distribution could further distribute the costs.
Of course providing basic support as well (like answering questions about using the software and perhaps helping the customer to decide which bugs are affecting them badly) would probably still be necessary, and could perhaps be done in a manageable way by selling the support on a "number of support employees available full-time to the customer" basis. Again, out of reach for small customers but probably a good proposition for enterprise-size ones.