Tsplines Replacement

a never ending topic here and discourse is full of it. did you use the search function at all?
here a few links i get when i search for t splines in your context.

rhino 6 will not have anything in its release but you can search for sub d in the search which is a wip function implemented in the rhino 6 wip.

in case you have bad luck finding anything for this either here you go