They took quite a few weeks to put SWR stickers over SWT names on the trains. Some of the curved orange line branded station signs still exist in obscure places, so could argue rebrand still ongoing.
SWR took over in August 2017, and nearly 8 years later there are still about 300 carriages still painted in SWT colours that are still in service (most should have been withdrawn years ago, but they retained them for now and kept old paint job)
So if current operator (SWR) never finished the rebrand in 8 years, who knows how long its successor will take.