"They concluded that the server was set to accept only incoming communication from a very small handful of IP addresses."
If it is true that there was not just communication but also ip address filters that protected this communication it would be an indicator for a ongoing and deliberate business relationship.
Also, there is evidence of ongoing human activity to protect and continue the communication:
1) When Alfa Bank and only Alfa Baink, not the Trump organization, was asked about the communication, the Trump organization decommissioned the domain.
2) The Trump organization then setup a new domain, apparently as a replacement, and Alfa Bank was the first to connect to it (or DNS lookup, I'm not sure of that detail).
I think there has been an interesting pattern with Trump. His choice of Manafort (Kremlin Insider) and Cater Page (Kremlin Insider), his daughter vacationing with Putin's Family, his son involved in business ventures in Russia. Trumps dealings with Russian Oligarchs concerning Real Estate in NY and Miami.
I suppose someone might find it interesting when a Presidential candidate has a great affinity for what some consider a foreign adversary and has taken deliberate steps in changing policy to align with Kremlin's/Putin.
If Trump is elected it will be interesting to see how it plays out with the Kremlin. Is he part of a 5th column?