But thanks to @Septfox for trying to pin down the answer, even if it's "we don't know".
Since the LTE band 71 has NOT shown up on US998 in FCC documentation, this probably means no. UNLESS:
1) LG submits a revised spec sheet to the FCC, which can be done. It would actually be in T-mobile's best interest for LG to enable that band on the "carrier unlocked" model. While T-mobile would not make money off hardware sales, they would gain additional customers who are considering switching. (Many people want a phone NOW, but need to get their ducks in a row family-wise to switch over to a new carrier.)
2) T-mobile radio can be flashed onto rooted "carrier unlocked" LG V30 US998. All the LG V30 hardware (antennas, etc) should be the same. At least from manufacturing efficiency it should be the same. Then it just depends on the firmware to enable specific bands.
T-mobile LTE band 71 (600 MHz) will also be available on "carrier unlocked" LG V30, not just on T-mobile's LG V30
LG V30 US998 will have ALL the U.S. carrier bands, so you can take it to any carrier you wish -- even T-mobile. Otherwise it would be pointless to have a U.S. unlocked carrier version if there were any carrier bands it did not have.
This is also the LG V30 model number that will be eligible for REAL bootloader unlock, unlike the recent T-Mobile LG G6.
T-mobile has LTE band 71 on their newly implemented 600 MHz spectrum and the LG V30 is the first phone to use that band.
While LG also releases "carrier unlocked" versions of their flagship phones, which qualify for REAL bootloader unlock and thus root, TWRP, custom ROMS, etc., no spec websites have listed LTE band 71 (600 MHz) on the upcoming carrier unlocked LG V30 US998. (While not yet announced, we know the model number because B&H Photo has a placeholder page and it matches previous "carrier unlocked" model sequences. It's also the model given to reviewers during the pre-announcement embargo period back in August.)
So, people assume and even T-mobile customer service reps have stated that to get LTE band 71, you must buy the T-mobile variant of the LG V30.
For people who want dev work, this was disappointing, because while T-mobile previously was dev friendly with either unlocked bootloaders or easily unlocked bootloaders, this has changed in the past year. I could give multiple examples, but the most relevant is the recent LG G6... The T-mobile LG V6 bootloader is ostensibly able to be unlocked, but not really. LG/T-mobile removed all ADB flash commands except for bootloader unlock.
Six months later, there's still no root (even with a 22 page root bounty thread), no usable TWRP and no usuable ROMs. Yes, some devs have ported ROMS for the T-mobile LG G6, but no one can use them. Meanwhile the UNLOCKED LG G6 phones have tons of dev work, because they qualify for REAL bootloader unlock.
A second subset of stakeholders are people who are considering switching to T-mobile (or T-mobile affiliated MVNOs) in the future. They would have to buy T-mobile LG V30 now to be future proof, as T-mobile will roll out more of this 600 MHz spectrum in coming years. The "carrier unlocked" model (which can be taken to ANY carrier) would not work for them, if it didn't have LTE band 71...
Then, yesterday, from the official T-mobile Twitter account, T-mobile stated that to get full 600 MHz experience, you could buy their LG V30 OR buy the unlocked version direct from LG.
Well, the unlocked version is LG V30 US998. And yes, while you can buy unlocked versions straight from LG if it makes you feel better, you can also buy them online at B&H, Amazon, even eBay.
IF TRUE, this is great news for the dev community and for LG V30 users. This is also NEWS because no other websites are stating this. And if T-mobile is officially stating this through Twitter -- just like they have officially announced many other things, why wouldn't it be true?
I've contacted one spec website for them to correct their now outdated information, and sent it to XDA News as it's big news.