We can easily communicate with a spacecraft on the Moon on the near side. The Far Side allows for a L2 halo communication relay satellite easily enough. How would a polar mission communicate with Earth, especially at a spot like the Shackleton crater? It seems like it would be difficult to see from Earth, and there isn't a convenient orbit like the L2 orbit.
ESA's unimaginatively named Lunar Lander mission, sadly cancelled in 2012, was a south polar lunar mission. They planned to use line-of-sight communications and just accept the periodic periods of communication loss.
Another mission constraint is the unavailability of an orbiter for communications relay. As a consequence, the potential landing site must have sufficient visibility of Earth to be able to send engineering and scientific data and to receive commands.This is generally achieved at the potential landing sites at the poles, where Earth visibility has a windows of approximately 14 days, due to the fact that the Earth centre follows a pattern of approximately ±6.5° in elevation every months, constrained to approximately ±8° in azimuth.
How would a polar mission communicate with Earth, especially at a spot like the Shackleton crater? It seems like it would be difficult to see from Earth, and there isn't a convenient orbit like the L2 orbit.
A constellation of three or more evenly-spaced relay satellites (the higher they are, the fewer you need) in fairly high polar lunar orbit would be sufficient to maintain continuous contact with sites near either pole. No such constellation exists today but it should be straightforward to establish one. Shackleton might require a few more satellites in the constellation to ensure that one is always above the crater rim, if constant contact is required.