Sigurd is confirmed to be a part of Cosmos in the Lostbelt? Nice. I don't keep up too much with Fate/Grand Order, but nice to see Sigurd getting some love. I think. I still haven't entirely worked out how I feel about him.
There hasn't been direct confirmation yet, but given the timeframe and Sigurd's own connection to Norse Mythology and datamined information on his voice actor, it's very likely that he'll be showing up for Lostbelt 2. They haven't done much with Brynhildr either but have been giving focus to all the other Prototype Servants so it stands to reason that Ophelia's Lostbelt will finally give her some focus.