XDCR : XMEM replication refused on 2.5.0 GUI on a mixed version(>=2.2.0) cluster

Scenario
-------------

• 2 node source cluster - one 2.2.0 and one 2.5.0
• 2 node destination cluster - both on 2.2.0.
• Try to create replication from 2.5.0 source node to dest cluster with version 2. <--Throws error
  "Attention - Version 2 replication is disallowed. Cluster has nodes with versions less than 2.5."
• Try to create replication from 2.2.0 source node to dest cluster with version 2. <-- Works

This comes from the following piece of code in menelaus_web_xdc_replications.erl :

check_xmem_allowed(<<"xdc-xmem">>, _) ->
case cluster_compat_mode:is_cluster_25() of
true ->
ok;
false ->
[

{<<"type">>, <<"Version 2 replication is disallowed. Cluster has nodes with versions less than 2.5.">>}

]
end.

Why are we disallowing replication with xmem for source clusters with cluster compat mode less than [2,5] ? By doing that, are we not missing this case where all nodes are >=2.2.0?