The Moral Parliament idea generally has a problem regarding time. If it is thought of as making decisions for the next action (or other bounded time period), with new distribution of votes etc when the next choice comes up, then there are intertemporal swaps (and thus pareto improvements according to each theory) that it won't be able to achieve. This is pretty bad, as it at least appears to be getting pareto dominated by another method. However, if it is making one decision for all time over all policies for resolving future decisions, then (1) it is even harder to apply in real life than it looked, and (2) it doesn't seem to be able to deal with cases where you learn more about ethics (i.e. update your credence function over moral theories) -- at least not without quite a bit of extra explanation about how that works. I suppose the best answer may well be that the policies over which the representatives are arguing include branches dealing with all ways the credences could change, weighted by their probabilities. This is even more messy.

My guess is that of these two broad options (decide one bounded decision vs decide everything all at once) the latter is better. But either way it is a bit less intuitive than it first appears.