This suggestion has been passed around a few times that he should be able to choose between his old gun, Destiny, and the new one, New Destiny, as his passive at the start of the game. The gun you pick changes your Q and auto attack style, with the old one holding the same basic playstyle old Graves had (Perhaps with Buckshot reworked to stop on first target hit, with reduced damage to for multiple hits on the same target), while New Destiny is the current kit.
This would change his play pattern significantly, and make him more of a flex pick, capable of being an early pick that can then be changed on where he is going, but would most importantly allow him to actually go bot lane again. His current kit can't ever go bot for a very simple reason. Every ADC down there can outrange him by at least 75 range, if not all the way up to 225 range, and his autos can't hit through minions so they just stand in minions and never get hit by him to auto-win all trades. If Old Destiny had 525 range, it would allow him to compete with other ADCs.
Or, if you want a wider scope rework that isn't a full revert that keeps his current kit as it's theme, you could let him swap guns at base any time, but be a more direct swap between Q and passive as current, keeping the ammo mechanic, with "old" destiny firing the Q slugs that leave the trail and detonate (with 525 as the base auto range, perhaps with the auto always going to max range regardless of target hit), and Q being the close up buckshot blast, or vice versa with New Destiny with the shorter cone autos and longer higher damage Q.
Assuming the basic Q damage mechanic (minus the AoE at the end) was used for Old Destiny, his autos could have a .9 TAD ratio on the first half, and a .6 on the second half, with both halves being able to crit independently. This keeps his kit friendly to his reworked E without needing to change it radically, and he'd have more reset potential on his E on his OD build in multi-target situations, but less in single target situations, or ND for the stronger single target at cost of range.