I don’t tour, so others will have better knowledge, but I still run 7 speed. With friction I not sure of what you want in an upgrade. I have always felt older Suntour was probably the best mix of stoutness and performance. I look back how I never appreciated the performance of my Suntour RD.
That said, the best derailleur setup I have, and still use, is the XTR-M900/910. I’ve picked up a few of them over the years. The set on my downtube shifting road bike was well used and sun faded and I bought it for testing. I’ve gone from double to triple, freewheel to cassette, and it just keeps going. I’ve got a couple of nicer ones, but who knows when I’ll use them. The downside is they have become super expensive over the years.
John