The PD20 R5 came out some time last year (don't know what month though.) I don't think there is anything within the next few months that will replace this light because none of the manufacturers have announced a new LED that can replace it. Fenix (as far as I know) does not have any plans of putting the larger XM-L LED in it because it would turn the light into a total flood light (a larger head is required to focus this large LED.) The smaller R5 LED gives this sized light a good balance between throw & flood, and fenix (along with other manufactures like 4sevens) want these type of lights to maintain good balance between flood & throw.
I was excited when companies came out with small lights with the XM-L LED's in them. I bought a Thrunite 2A just to try one out. It has roughly the same sized head as the PD20, but with the larger XM-L in it, the light was almost a pure flood light. I didn't like it. Others love the floody little light, but I just didn't (YMMV.) I think this is why you won't see companies like Fenix or 4sevens use the XM-L in many of their small lights (maybe a few lights, but not a whole line of their lights.)