Need ideas for subclass features

Hello all, I'm working on a homebrew rogue subclass for one of my players right now. I'm pretty happy with what I have so far, but I'm struggling to come up with ideas for the 17th level feature. Any suggestions would be much appreciated!

Here is everything I have so far though:

The Mimic subclass

Having sampled the many roads of life and the people who walk them, you have observed an abundance of people and how they get by. A ship's captain yelling over a storm to direct the crew as they steer from the helm, a politician convincing their people that an innocent man murdered someone they killed instead, a thief stealing priceless paintings only to replace them with worthless copies, a smith checking chunks of ore for the best ones to use for their next project; you know them all, and picked up their skills with ease. Now after all your wanderings, you use these various talents and personas as needed, switching between them like second nature. Hiding in the shadows or blending into a crowd is one thing, but few can ingratiate themselves into any inner circle of society. Knowing people is your game, and being one of them what you do best.

Chameleon's Guise, 3rd-level The Mimic feature

After observing master crafts folk, sea captains, snake oil merchants and more, expertly using their skills, you've grown accustomed to appropriating their abilities to better match those you wish to fit in with. At the end of a long rest you can choose one skill or tool you are not proficient in and gain proficiency in it for that day.

-At 9th level, increase the proficiency to expertise if selecting a skill you are already proficient in, and allow for it to change after a long and short rest

Staged Preformance, 3rd-level The Mimic feature

You are able to convince nearly anyone of who you might be and what you can do, even yourself. Even at your worst you put others at ease, allowing you to get away with minimum consequences. When rolling for Persuasion or Deception, you may treat any roll of 7 or lower as an 8. Your naturally convincing act also negates any disadvantage on these checks due to the opposing creature's hostility, or previous failed rolls from other creatures.

Spellbinding Persona, 9th-level The Mimic feature

Grant once a day usage of the spells: Arcanist's Magic Aura (2nd level) and Mislead (5th level).

Treachery, 13th-level The Mimic feature

When you first attack a creature you have made a successful charisma check against (Persuasion, Deception, Intimidation) within the last hour, your Sneak Attack dice increase to D10s. If the relevant charisma check affected multiple creatures, this feature only applies to the first creature targeted, as it reveals your true intentions to the remaining group.

If an ally within your melee range hits an enemy with a weapon attack on a creature you have made a successful charisma check against (Persuasion, Deception, Intimidation) within the last hour, you may use a reaction to assist them. In addition to whatever damage they are already doing, they gain half of your normal Sneak Attack dice in damage, rounding the total up. 

You may use this feature either way, but may not use both aspects of it against the creature(s) affected by the same charisma roll.