One impediment to many for the Williams products is the fact they don't have any command models.
A few years back I upgraded a Williams scale GG-1 to TMCC.
Electric RR Co upgrade for Williams GG1
A bit more recently, I upgraded the Williams 44-ton locomotive to TMCC.
Williams 44-Ton Upgrade with ERR CC-Lite, Sound, & Electrocouplers
I've done a number of the Williams brass steam upgrades for various folks, and even one or two for me. I have several waiting on the shelves for an upgrade now.