The math doesn’t quite add up.

An iPad Pro 12.9 is 1 lb 6 oz. Add a Magic Keyboard and Canopy and it’s 2 lb 4 oz. And your iPad is now naked and lacking a case, so add the Smart Cover. 2 lb 13 oz. Add a Magic Trackpad to all of that and you’re now up to 3 lb 5 oz.

OTOH, an iPad Pro with the iPad Magic Keyboard cover is 2 lb 15 oz, or just 2 oz heavier than the iPad with keyboard, Canopy, and cover.

So unless you can find a mouse that weighs less than 2 oz, all of the assorted pieces and parts ends up weighing more than the iPad Magic Keyboard solution, and that’s without Magic Trackpad support.

Or to paraphrase a common quote: I don’t think you’re saving what you think you’re saving…. ;)