While no one knows for sure when RTX3000 and Big Navi will release, some things point towards September and launch dates that are very close to each other.
This is known, or rumoured rather, because of a piece done by "rogame" on Hardwareleaks.com where the well-known and twitter-happy leaker has revealed a lot of the more specific details.
Navi21 is the largest RDNA2 based GPU, using 80 compute units, and 5120 GPU cores, 50% better performance per watt, and a 505mm2 die size. There will be both Gaming, Pro and Apple variants.
The Gaming variants are XTX, XT, XL and XE. They will tier-wise be similar to RX5700 XT anv. Ed., RX5700XT, RX5700, and RX5600XT. The Pro variants will be Pro-XT and Pro-XL, similar to w5770X and W5700 tier-wise, and Apple versions will be XTA, XLA, Pro-XTA and PRO-XLA.
There will also be a Navi 23 lineup, as well as a Navi 10 refresh, with XT+, XM+ and XTE+ replacing RX5700XT, RX5600M and RX5600XT.