My solutions are:
1. Reduce arena income
2. No TV revenue that week
3. Reduction in merchandising
I stole them, I know, but mine are simpler.
I think you're in the right direction. I think something like:
1. Loss of TV revenue for each walkover, with perhaps escalating amounts for repeat offenders.
2. Loss of all training benefits for the week for each walkover (so players are treated as having played 0 minutes).
3. After a second walkover in a season, a very long-term negative on the fan survey (perhaps 2-3 seasons).
4. When calculating draft position, count each walkover as a win rather than a loss, and for tiebreaks for draft purposes, a team with no walkover gets the better pick.
That should hopefully eliminate most if not all of the reasons anyone would give an intentional walkover and be a harsh reminder to teams that do so accidentally to ensure it won't happen again.