We've discussed this request internally and with the moderators and we decided that there's universal support for this request and so I've just made Mast a moderator on this site, joining Sᴀᴍ Onᴇᴌᴀ and Peilonrayz as a third winner of the election.
Just to throw a few things out there... having an odd number isn't usually a big deal - most of the time, mods don't circle up and vote about actions, though they may ask for feedback before doing something - so we don't really take that into account.
We also don't really see the number of slots as "fixed" based on any metrics - so (for example) we don't say "y'all get 200 flags a month, and we expect 50 flags per mod per month, so you need four mods". We have the number of mods that are needed to get the work done. If the mods on a site are comfortable with their workload with the number of mods they have - that is what's important.
If they feel like a new mod is needed for any reason, we'll see why they're asking and use that to prioritize scheduling an election. So, if they're getting bombarded with flags and someone just started a new job and needs quick relief, they might get an election right away. If there's a longer term "we'd like to have a new face on the team", it may wait a month or two.
Since y'all just had an election, it's easy enough to add a new moderator - as long as there's support for it and there's more candidates - what we set a pretty clear limitation on is that we can't "call up" the last person in an election - so if Mast had been the only other candidate, we wouldn't likely have added him to the team because we need elections to be competitive but, since there were two others, there's nothing preventing this on our end.
So, welcome to Mast - may you serve joyfully and well. :)