Only Apple knows for certain, but if there are newer, internally tested Vega 64 drivers that Apple feels are stable enough to update the iMac Pro, then it will include them in a future update. Whether that will be 10.14.5 or a more distant update is Apple knowledge alone. As a fellow user, I cannot speculate about internal Apple product planning.
I guess the real question is what initiated those System crashes, and was it something else in Adobe Premiere Pro than Vega 64 support, or something else unrelated to Premiere Pro.
Feel free to run an EtreCheck assessment of your iMac Pro, and post the results in the Note tool:
EtreCheck will deliberately conceal any privacy information, and is regularly used in these support communities to determine if there are other drivers/software causing interference with normal operating system, and application behavior. On Mojave, if you are given the opportunity to grant EtreCheck full drive access, do so, as it can provide more information than otherwise.