Yep for now you have to do it on your own. I did some tests with a very simple approach which might work for you.
The idea of host migration is to select a new host when the current one drops out of the game, the problem comes when you are not able to select the new host or you do not know where to connect when your current one drops. So what I did was to pre-select the best host, this will be done every time a player enters/leaves the match. Once a auxiliary host has been selected (you can implement quite a range of selection mechanisms such as a so called [two-phase commit protocol](two-phase commit protocol) to select the next usable host) you will send the connection info to all other clients which will now to whom to connect in case the current server drops out. You can also use a back-end server which could perform the selection but my previous proposal does not require such an infrastructure. The most difficult part is to rebuild the game on the new server, so when a client converts itself to a server you MUST save the data of all other clients using the FUniqueNetId to identify them (an example on how this can be done is the InactivePlayerArray of the GameMode which is used to hold the data of players that drops and connects again to the match) and the GameState.
Hope this will help you a bit in getting it working for you.