My friend is starting a campaign soon and we were discussing of going with a house rule that you can use a bonus action spell and a first level action spell in one turn rather than just a bonus action spell and and a cantrip. Would that be too crazy or not?

Probably not. Most bonus action spells either are support/control or power up weapon attacks (which will require a weapon attack anyway).

I think the rule was made to nerf the quicken spell metamagic of the sorcerer, and possibly to prevent widespread healing at low level.