If, hopefully, RDNA2 does scale down good with TDPs (TGPs? These new ways of measuring consumptions is quite confusing until they standardize somehow again), we could expect a 75W 6500ish LP somewhere in the pipeline.
Mind you, AMD has yet to announce anything below the RX 6800, as of now, a 6500/6600 is nothing more than wishful thinking. Having said that though, cheaper GPUs are an important market, expect AMD to offer something in the low spectrum of the lineup, sooner or later.
TDP = Thermal Design Power, a vendor-defined metric for ensuring coolers are capable of keeping it within thermal spec. Used as a shorthand for power draw simply because it's been equivalent to that for ages
TGP = Total Graphics Power, AMD's spec for the power consumption of the GPU ASIC alone (not VRAM, VRMs, and other onboard components)
TBP = Total Board Power, AMD's spec for combining GPU ASIC, VRAM, VRM and other on-board GPU power into a single power draw spec. Equivalent to what most people mean when they talk about the "TDP" of a GPU.
Yes, it is confusing.
As for new LP GPUs: as you say, hopefully with the increased efficiency of RDNA 2 we should get some new 75W GPUs, but I wouldn't expect them until late next year at the earliest. Still, with the 6800 XT at 300W and 6800 at 250, expecting a 6700 XT at ~200, non-XT at ~175, and so on should open the gates for some nice 75W GPUs around the 6500 (XT) class. If they are generous and go for a slightly large die with lower clocks and keep some form of Infinity Cache it could be a real beast. Lower-end Ampere might arrive a few months earlier, though given the meagre efficiency improvements over Turing that might not change all that much.