Before any meta arbcom could be formed it would definitely need a strong definition of its jurisdiction.
I just wanted to make a comment for consideration about electing people to it. I may not be the only person concerned that it would be a strong concentration of power, and therefore a magnet to those who seek power, and that the people who most should be on it may be discouraged from actually participating due to the politics it will attract.
I think a somewhat jury-like system could work. Have a large group of potential arbiters and then for each case a selection of them are chosen to work on it. It would need a small group of non-jurors to organise it.
Would-be jurors could either be self-appointed (ie you add your own name to an appropriate list on meta), or community-voted (I would expect the standards to be much lower than e.g. steward elections because the idea would be to have dozens of potential jurors), or maybe self-appointed combined with some wikimedia requirement (admin on any project, or 6 months + minimum 200 edits on any project). (I would also expect that in either way, potential arbiters would have to regularly reaffirm their commitment, e.g. have 6 monthly periods of commitment, to avoid the problem of people leaving the projects and their commitment being like a ghost.)
You could even have a system where people nominated areas of expertise (e.g. languages, bots, various projects, various policies, coypright/legal), and then for each case, half the jurors could be chosen randomly from people who had expertise in the relevant area/s, and the other half could be randomly chosen from people who did NOT have expertise in those areas. However that could be a bit problematic in itself, in who decides what the relevant areas of any case are.
The benefits of this approach would be that they reduce the concentration of power, allow much wider participation, and massively reduce the potential for "burnout" among active arbiters. The drawbacks could be inconsistency in decisions from one case to another, but having minimum guidelines that potential arbiters must agree to, or voted-on arbiters rather than self-nominated, could minimise that.
cheers Brianna