I wouldn't get my hopes too high.
Thieves in Time was a financial failure, and it'd be relly hard for Sanzaru to get the budget for Sly 5. I think they were idiots by making a cliff hanger ending, especially when Sly had been dorment for 8 years.
You just can't jump into the assumption that the revival of a video-game character will be successful and earn the budget for a sequel.
It's all on the hype, and Thieves in Time had none.
Now officially addicted to League of Legends.
Send help.