Hey David,
the Onefinity Journeyman has the opening on its 4′ side, so you could tile any 4′ wide sheet with it – you could at same time hope that the Y upgrade to 48″/4′ will be there one day. The X upgrade to 48″/4′ was also hoped for a long time, and then suddenly it was there.
I also find it sad that there’s still no 48″ Y-50 mm rails kit offered which would enable to assemble a 4′×4′ machine, but since it would be made of parts that already exist today at the manufacturer, I would not exclude that they are offered one day. It is a feature requested frequently (however never commented by the manufacturer, as far as I remember).