Johnson to EU: Let's replace Irish backstop with commitment to alternative arrangements

And what if alternative arrangements have not been agreed by the end of a transition period? Does he really not understand the purpose and necessity of the backstop?

How about returning Northern Ireland to... Ireland?

Returning Northern Ireland to Ireland would indeed resolve this problem, and it would be welcomed or accepted by most parties. But it would need the agreement of the NI protestants, currently a non-starter.