As somebody who usually plays cleric, I don't mind each god being open to each domain.
It's an issue when you are allowed to choose domains that your deity is opposed to, such as Light for Shar or Trickery for Tyr or Torm. The deity wouldn't grant such a cleric any spells or the Channel Divinity feat.
The issue isn't whether a Tyr cleric can choose Light instead of War, but when a cleric wants choose a domain their deity would be utterly opposed to. The PHB lists the availabe domains for most deities for a reason. It is required to preserve the integrity of the setting, in this case the Forgotten Realms.
I'd also love to see deity choice being tied to domain choice and in some cases to race as well.
I have always seen religions as a social, rather than racial, construct. So if my dwarf cleric has grown up and trained a major dwarven settlement, she is likely yo follow one of the dwarven gods. If, however, she is born and raised in a human settlement, she might follow the religion of her parents or decide that one of the human gods better reflects her own worldview.
Just as you have Western people following Eastern religions in the real world, so the D&D religions should be open to any race.
Note that I said " in some cases", as the Faerûnian pantheon would still be open to all races as it should.
But the racial pantheons should not be open to anyone not from that race, there simply wouldn't be a dwarf following the Seldarine (elven gods) under normal circumstances.
