This is already possible with
Whirlwind Kick on a Skin Druid. Druid transforms into bear then casts the spell - as a bear! Fun interaction.
Hmm. I have dismissed of the Whirlwind Kick spell as weak when I looked at it, but let's check the benefits thereof.
Let's say a level 6 Druid wild shaped into a Cave Bear casts Whirlwind Kick. Strength 20 gives +5 damage modifier, and we'll assume a Wisdom of 18 (+4 modifier) so a melee spell attack modifier of +6 with the +2 proficiency modifier added in. However, unarmed strike damage is only 1 + Strength modifier (A5E core rulebook page 309). Hence, you are doing one +6 attack at targets in a 60' line, inflicting 2d6+6 (13) damage if you hit them. And if the targets fail their Dexterity save, they are either pull 10' closer or pushed 10' away, your choice. As the spell is written, I assume it is a single melee spell attack roll, so you run the risk of missing all the targets if you roll low.
The damage of Whirlwind Kick is less than that of
Call Lightning, 3d10 (16.5) with Dexterity save for half; significantly worse when we consider that Whirlwind Kick only inflicts damage on the round that you cast it. Call Lightning lasts 10 minutes with concentration, but is only 5' radius on each lightning strike as an action. Situationally, you should be able to line up 2 opponents to Whirlwind Kick them, and may hit a similar number of opponents with Call Lightning. Whirlwind Kick is range self, so in A5E it can be cast in wild shape, and it does have the benefit of battlefield control moving opponents around. Call Lightning also has the limitation of not being usable without a 100' space above you.
Edit: Whirlwind Kick is a 15' wide area (not 5' as I had initially assumed), so can hopefully hit 3+ foes.
So in my opinion, Whirlwind Kick as written is a little weak for a 3rd level spell, albeit maybe worth casting in wild shape. I think part of the problem is the typically low unarmed strike damage (i.e., 1 + Strength modifier) that a Druid has. Now that said, it does pair better with an Adept/Druid build, or other builds that have an improved unarmed strike damage die. As such, it would benefit from the martial art die damage scaling with the Force of Nature synergy feat that I am proposing.
I think it would be reasonable to allow a Druid to use their natural weapon attack damage die instead of the unarmed attack die with the Whirlwind Kick spell. For example, a level 6 Druid Skinchanger in CR 2
Plesiosaurus form would do 2d10+2d6+4 (22). That's still significantly less than an 8d6 (28)
Lightning Bolt with Dexterity save for half.
Do any DM's permit substitution of natural weapon damage dice instead of unarmed attack die for Whirlwind Kick? Seems like a natural pairing of the spell with wild shape.

Plesiosaurus is the highest damage natural weapon attack that I found for a CR 2 beast or plant in my list of good CR 2 wild shapes.