I also support hotseat multiplayer, as do a lot of my friends who are MOO2 veterans. I am more amenable to buying 4X titles without it (and have been sadly disappointed with lots of them the last years, to be honest), but for them it is a vital feature which determines if they even will give a new 4X title a second look.
I think the developers still underestimate the snowball effect of the people who care enough about the feature to post on this forum. If hotseat is included in GalCiv3, people like me will tell their 4X veteran friends about it and, if the game is good, there is a much higher chance that they will buy it, thus reaching the audience of veterans who still yearn for a new title to take up the flag Master of Orion 2 has held up for so long.