Adobe Photoshop Lightroom resampling is a hybrid Bicubic algorithm that interpolates between Bicubic and Bicubic Smoother for upsampling and Bicubic and Bicubic Sharper for downsampling. Lightroom and ACR uses a adaptive bicubic algorithm: the algorithm parameters are chosen automatically based on the relationship between the original image size and the final image size. These parameters were determined empirically by doing lots of experiments with photos being resampled to common output sizes, such as web-sized images (800 to 1000pixels on the longer dimension), small prints, and big prints. I can see slight improvement over the same resizing using various Photoshop algorithms.
Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"
Well that's certainly good to know. Thanks to you both for the quick reply. I consider Preserve Detail 2.0 to be the gold standard in the Adobe world and have regarded the others as inferior for serious resampling jobs (more than 2x). This of course requires a trip into Photoshop, which is not a big deal, but if it can be done in LR, why not? I guess I'll continue my present workflow.
You may also be interested, if you haven't already come across them, in LrC's AI "Enhance" and also Super Resolution doubling - the same options being also available within ACR. This kind of approach goes beyond just the resizing algorithm because it modifies the demosaicing and conversion itself - (I have presumed here, perhaps wrongly, but judging by your reply, that you are principally interested in upsampling beyond the in-camera resolution).