As it currently stands, attempting to select an enemy hero who is hidden by the fog-of-war by clicking their portrait at the top of the screen yields nothing. When the hero becomes visible, clicking their portrait at the top of the screen will select that hero and show their current level, items, health and mana.
My suggestion would be to take the first case, when the enemy hero is hidden in the fog, and to show a 'dummy hero' upon clicking their portrait at the top of the screen.

The dummy hero would show the following and only the following:
- Current Level
- All abilities, does not show current level or cooldown
- Current stats according to what that hero at that level would have (a level 10 riki would have X amount of HP, mana, int, etc.)
- Hide all items in backpack and inventory.
- Do not show 'last known' items .

All the information the dummy hero would present would be information that could be attained by either opening the scoreboard, or simply knowing the enemy hero. It would allow uninformed players to click a hero that is not currently visible to see the enemy hero's spells.

When the selected hero is revealed, the selection can change from the dummy hero to the real hero and show information normally.
If a player were selecting the real hero which went into fog, the current method of showing last-known status would be sufficient and would not change any current functionality.

To help illustrate the use of this feature and a possible case in which it could be useful, here is the following hypothetical situation.

The enemy Magnus recently used their ultimate Reverse Polarity and is currently dead. Your team decides to push into the enemy high-ground. As you group up and approach the high-ground, you have to make the decision on whether to fall back or not if the enemy Magnus buys back. You click the enemy Magnus portrait at the top of the screen. Since he is currently dead and therefore not visible, a dummy Magnus is shown. The player can read the skills of the dummy and notes that cooldown on Reverse Polarity is 120 seconds and luckily, since one of your teammates noted down the time he used it, a bit of quick math shows that his ultimate is on cooldown for another 60 seconds. Your team pushes with the knowledge that the enemy Magnus for certain will not have his ultimate if he buys back unless he uses a Refresher.

While it is a bit far-fetched to say that one entire team wont know the approximate cooldown for a high impact ultimate such as Reverse Polarity, the feature can still be useful as a learning tool. At the start of a game a player can refresh themselves on specific skills the enemy has before they even show.