This is early days and we don't yet know why Softbank bought Fortress Group and what they want to do with it.
Quite possibly this has nothing whatsoever to do with Brightline and it may not have any effect whatsoever.
Whether it has anything to do with it or not is a different question than what impact it will have. FIG was, as far as I can tell, comparatively strapped for cash and so their ability to self-finance was limited. As a note, per their last filing period Softbank had about $22bn in cash and equivalents in the bank while FIG never had more than about $400m.