No change in behavior. Replacing references with pointers allows Node interface creation to be delayed until later during gui startup next commit to support implementing -ipcconnect option
Partial backport (3/4) of bitcoin-core/gui PR35:
https://github.com/bitcoin-core/gui/pull/35/commits/102abff9eb6c267af64f2a3560712147d1896e13
Depends on D8654.