Shen is a project we are currently actively working on. We want to not only just buff Shen though, rather we are attempting to take this opportunity to experiment with some gameplay changes that would make Shen more fun to play overall.
On Live, most of Shen's fun comes from the power and feel of his ultimate as it controls the flow of the battlefield. While that is awesome, we want to make sure Shen players can have interesting gameplay while his ultimate is not up. On Live, this gameplay currently consists of Shadow Dashing into a fight hopefully taunting the right targets, expending the rest of his energy rapidly by choosing to use Vorpal Blade or Feint, and then standing around looking pretty with no Energy for the rest of the fight.
The #1 issue we want to resolve with Shen is to make sure that he can have a sustained threat presence/utility in late game team fights. In my opinion, this starts with addressing his current Energy issues. Imagine a Shen who can Shadow Dash 2-3 times across the battlefield per fight, first locking down enemies and then returning to the aid of his allies to thwart off attackers. Not that this is necessarily exactly what we'll eventually do, but these are the kinds of thoughts we are currently toying with.
At the same time, we want to make sure that we keep Shen's extremes in check. For example, top lane Shen actually has a ton of sustain and early on can out harass / out lane many of the popular top lane champions used today. It can be an extremely frustrating experience. Another pain point in playing against Shen is the dreaded side push strategy in which he forces one of your team to stop him and then suddenly teleports to the team fight making it a 4v5. Although these are valid strategies and situations Shen excels at, we want to make sure opponents have the necessary counterplay options to fight against them.
These are the types of issues we are tackling while working on Shen, and unfortunately it does take a good amount of time to get right, especially with the multitude of other projects going on.
Pertaining to Mundo, we do intend to eventually make changes, but he is not an active project at the moment. The main issue we would be looking to solve on Mundo is assessing his early vs. late game potential, which would probably involve giving Mundo access to some more utility. At the same time, I think we would take the opportunity to solidify the risk vs. reward gameplay surrounding Mundo being at low levels of Health, constantly teetering back and forth to create advantages and bait enemies in.