I don't see why there should be a problem with ranking points...they aren't ranked together and can use separate systems.
The ATP revamped their ranking system several years ago, so there’s no reason they can’t do it again, in conjunction with the WTA, if need be. Ultimately, though, I don’t think having the same ranking points is absolutely necessary. At the very least, it shouldn’t be the thing which brings the whole process to a halt. But it would be helpful for fans to learn one system, instead of two.
...the pay isn't even "equal" tournament-to-tournament in the men's game or the women's, is it?
Yes and no. For the WTA, the prize money is usually the same (or close) among tournaments in certain categories. For example, tournaments in the “International” level (more or less the equivalent of an ATP 250) generally have the same total financial commitment ($251,750), but “Premier” (like an ATP 500) tournaments vary. Prize money in the ATP has no consistency. Some 250s (such as St. Petersburg) go as high as $1.2 million; the same week, prize money in Metz is about half that.
Since there isn’t strict uniformity within either the ATP or the WTA, this factor also shouldn’t be what prevents them coming together.