Motorola has a very mixed record so far with their updates. The OG Droid was actually quite good at getting updates in a timely manner and only trailed the Nexus by a few weeks. After Motorola switched to Blur though for all their devices they lagged behind by a few months and even though with Jelly Bean they removed most of the Blur apps in favor of stock, that was still nearly what 9 months after 4.1's source was released before the Razr, Bionic, Droid 4 all got it. In fact for a while there they were one of the slowest at releasing their updates.
Now the Moto X is a new beast though and different from what Motorola has done now so it's hard to say. All the previous devices were part of the "old motorola" and the X is the first device of the "new motorola". The X is almost pure stock so there is very little tweaking that will need to be done. They just need to add in support for their Camera App, Active Display and Touchless Controls, do any kernel updates/bug fixes and then test/resolve any new bugs that popped up in 4.3. Motorola has said that an update is in the works and will come out soon with many improvements for the Moto X. Is this 4.3 or just a newer 4.2.2 build? We don't know.
I'd like to imagine that we will see 4.3 released sometime between now and early October on all carriers considering Samsung announced they will begin to roll out 4.3 to the SGS4, SGS3 and Note2. If Motorola is the first to release a stable, solid build of 4.3 for their new X8 devices and continues to keep up with their updates in a quick and timely manner, it would do a lot to rebuild their name. Right now we just have to wait and see if Motorola is serious about getting better about releasing timely updates or not.