Only if the R1 is a high MP camera. If the R1 has 24-32 MP I would consider the R3 and R1 too close unless there is some other key differentiator (that I cannot think of at the moment).
R3 uses SD card slot, whereas the R1 will likely have dual CF Express, this makes the R3 more compatible with the R6/R6II. This is relatively minor, however, the R3 can be bought now for 4399 euros and the new R1 will likely cost 6999 or more in Europe when new (could easily be a grand higher), so basically cost of R3 + R6II (less than 2 grand for body only now as grey market import).
Wedding photogs like shooting with dual strap harness etc., and the R3 is around 1 Kg (less than R5 + grip). The new R1 weight is not known, but will likely have more features than the R3 and may be a slightly larger form factor - could weigh something like 1.25 Kg (1DX III is 1.44 Kg). Again, we are guessing.
So really price, size and weight. Presumably R1 users will be using a single body, coupled with a long lens. Although many events/wedding pros did shoot with the 1DX in the past, some DSLR shooters probably still are. I still believe the R1 will have some unique feature, like shooting at 50 frames per second in burst mode, possibly something like fixed internal storage (mini NMVe type that could act like buffer expansion). Just as the R5 was marketed heavily as an 8K video camera (yes..everyone says that was a poor marketing tactic given the heat issues), the anticipated R1 will have something special...what?..no idea yet.