The effects of changing the mana system like this are far reaching enough that I would try other things first. For example, upping the number of free mulligans mostly deals with mana/colour screw. If flood isn't something you think can be handled enough through deckbuilding then you can add something like letting players pay 2/3 to exile a card from their hand to draw a card.
That isn't to say what you're suggesting is bad, but there are too many changes to know how gameplay would change. For example, is aggro weaker or stronger? Aggro never needs to draw a 4/5th land, which is hard to understate the importance of, but at the same time slower decks will essentially never stumble on mana or tapped lands. Slower decks can also play their higher cost cards as lands, so aggro loses the card advantage of having those cards stuck in their opponent's hand. In a similar vein sideboard cards are way better to maindeck, since you can just play them as lands, and a lot of sideboard cards are anti-aggro. So is aggro better or worse off? This system also ups the complexity of the game significantly since deciding what card to play as a land is not an easy one and you're not playing 17 textless cards.
I'm personally not too enthused by this system since it de-emphasizes deckbuilding a good bit, but I understand not everyone enjoys pulling up the chances of playing a 1CC card on t3 and altering your deck to manipulate that number as much as I do.
That isn't to say what you're suggesting is bad, but there are too many changes to know how gameplay would change. For example, is aggro weaker or stronger? Aggro never needs to draw a 4/5th land, which is hard to understate the importance of, but at the same time slower decks will essentially never stumble on mana or tapped lands. Slower decks can also play their higher cost cards as lands, so aggro loses the card advantage of having those cards stuck in their opponent's hand. In a similar vein sideboard cards are way better to maindeck, since you can just play them as lands, and a lot of sideboard cards are anti-aggro. So is aggro better or worse off? This system also ups the complexity of the game significantly since deciding what card to play as a land is not an easy one and you're not playing 17 textless cards.
I'm personally not too enthused by this system since it de-emphasizes deckbuilding a good bit, but I understand not everyone enjoys pulling up the chances of playing a 1CC card on t3 and altering your deck to manipulate that number as much as I do.