Hello from a longtime lurker! I'm not planning to attend, but here are some thoughts from my biology geek side.
Coronavirus data for Minneapolis' surrounding county at https://covidactnow.org/us/minnesota-mn/county/hennepin_county shows Rt well below 1.0 and 60% full vaccination, which is pretty good.
I figure if there is no post-july-4th surge in the next couple weeks, it should be safe for fully vaccinated people to attend. See https://events.linuxfoundation.org/open-source-summit-north-america/attend/h... for an example policy the event might want to adopt (or who knows, might already be required to adopt, dunno about xdc governance).
Also, rules for international travel are complex. Being fully vaccinated is strongly recommended and a specific kind of proof of vaccination and a recent specific test result may also be required; see e.g. https://www.cdc.gov/coronavirus/2019-ncov/travelers/international-travel-dur... https://reopen.europa.eu/ I suspect travellers may need to obey rules for both origin and destination countries... - Dan