Are lookup textures still used for anything? I know in the not so long ago (5-10 years?) that it was popular / efficient to bake data out into textures and then read the data from the textures, often using the built in texture interpolation to get linear interpolation of the baked out data.

Now that computing time is cheaper compared to texture lookup time, this practice has definitely lessened if not all together disappeared.

My question is, are baked out textures still used for anything?  Does anyone have any usage cases for them in modern architecture?  Does it seem likely they will ever make a come back? (say, if memory technology or basic GPU architecture changes)
Yes, lookup textures are still used. For example, pre-integrated BRDFs (for ambient lighting, say), or arbitrarily complicated curves baked down to a 1D texture, or a 3D lookup texture for color grading, or a noise texture instead of a PRNG in the shader.

ALU is generally cheaper than a texture sample, true, but you still have a limited amount of ALU per frame. GPUs are good at latency hiding and small lookup textures are likely to be in the cache. If your function is complicated enough, it may still be worth using a lookup texture.