Men have had their own boat race for almost two hundred years. Why shouldn't women get a race of their own too?
Rowing is a subject close to my heart (though none of this river crap, I row on the sea 
), so I have a few thoughts about this from a technical / opinionated afficianado POV. Firstly, rowing is above all about the eight rowers working as one machine. You want everyone not only dropping their blades into the water and pulling them out at the same time, you also want them all to be pulling the exact same distance within the water at exactly equal pressures. It is not vital, but very helpful, that the crew be evenly matched in terms of height and therefore reach. If you have a crew of seven tall people and one relatively much shorter person that person is going to have to adapt their stroke, possibly moving forward quicker on the recovery (when the blade is out of the water) to ensure they have the same 'reach' as their crewmates. But this will then mean that they aren't moving in perfect synchronism with their crewmates and will subtly throw off the rhythm of the boat. So, if the boat race was 'genderless', as you say, the crews would probably continue to be very tall people, thus excluding more women than men.
A third, mixed race category would be great, and would probably see smaller/lightweight men getting the chance to row with women of similar sizes etc.
From the point of view of watching the race, I'd also much rather see two or even three races rather than just the one. Different crews of different sizes and genders row very differently - there's more than one way to skin a cat etc! - and I love observing that. You can row with pure weight and strength and move pretty fast, but lighter crews can often be incredibly technically proficient and a real pleasure to watch if a perfect rhythm in a boat is the sort of thing to give you goosebumps. From a rowing fan POV, the more races, the better.
Finally, there is a certain irony to arguing the semantics of 'true equality' w.r.t. the Oxford and Cambridge boat race. Within the context I think bringing the women's race up to the same status is fabulous, but within the wider picture there are other issues to mull over if you want a deep discussion about equal access etc.