They won't have to deploy midband RRUs to meet deployment requirements since 600/700/800 travels further, and the tech is the same for both. Midband will be solely a capacity play, since that'll get them 40 MHz of downlink and 15 MHz of uplink in most areas (see https://www.fiercewireless.com/wireless/wake-doj-deal-where-dish-s-spectrum-and-how-much-does-it-have). That's on top of low-band, which after n26 comes online will be 20x15 (albeit split over three different bands) at least, and a symmetric amount more in some markets. With a comparatively minuscule customer count, the network should fly with that amount of spectrum.
My guess is that in three years Dish won't have touched 30% of the US population, so T-Mobile will be able to renew 600 licenses in those areas uncontested, including in plenty of rural areas, for another three years. For the remaining 70% of the US population (which will be a pretty small % of territory, so a rather small number of licenses), there'll be areas where Dish will try to squeak by with a low-band-only build, and *those* are the areas they'll be compete more on for spectrum leasing. For areas where there's enough traffic to build out mid-band, Dish may or may not need the extra 600...and those are probably the same areas T-Mobile will have a blanket of n41...so competition for that spectrum may be a bit more tepid, with the winner being whoever has more 600 sites lit since site density will determine capacity.
One interesting thing to note here: Boost already sells a phone that's (partially) compatible with Dish's upcoming network: the S20 (n66 and n71). In pure dollar terms, they're subsidizing that phone the most our of their entire lineup, selling it at $720. Still spendy, but at least they'll have *some* phones in the field that support the new network, and as time goes on they'll be able to sell the S20 for cheaper. Assuming they're okay with folks dropping down to T-Mobile LTE for voice since the X55 modem can't do VoNR, and sitting primarily on n71 because the phone can't aggregate NR-NR.
It's probably worthwhile for them to get a variant of the S20 recertified with n70, as that's adjacent to bands 66 and 25 so radio performance should still be fine. That would give the S20 access to their full native mid-band network on a phone most likely to be picked up by the folks who'd use the most data on their network.
With all that said, I would *not* expect Dish to pick up any more 5G phones until they're able to get one with an X60 or equivalent modem; having a network spread across slices of five bands from the get-go means NR-NR aggregation is important, and it'll take VoNR to keep phones from dropping down to roaming on TMo to make phone calls. So I don't expect Boost will get the A51 5G or A71 5G...better to sell LTE-only phones and then introduce phones with better chipsets later, to avoid heavily subsidizing phones twice.
Then, once you've got a $400 phone with VoNR, sell bundle it with two months of unlimited-everything service and you're off to the races. I figure we'll be at that point by this time next year, at which point I'll probably pick that phone up to see what Dish's network is like...as long as they allow tethering at full speed.
They have ordered triband n71, n26 and n29 low frequency RRUs and dual band n70 and n66. Something tells me that they will deploy the lower band first and then deploy enough of the midband RRUs to meet the deployment requirements. Of course I expect them to deploy first in the urban areas then suburban. Overall I think they will live within their means as far as deployment, shielded by the roaming agreement with t-mobile.
For me the interesting event will happen in 3 years when T-Mobile's leases with other holders of 600Mhz spectrum expire. Will we see a bidding war between T-Mobile and Dish for those leases?