Moore–Tachikawa conjecture for the Kostant slice

Let $G$ be a connected semisimple affine algebraic group with Lie algebra $\mathfrak{g}$. Let $\mathrm{Kos}\subseteq\mathfrak{g}$ be the Kostant slice associated to a principal $\mathfrak{sl}_2$-triple in $\mathfrak{g}$. The isomorphism class $[G\times\mathrm{Kos}]$ is a morphism from $G$ to the trivial group in the symmetric monoidal category $\mathbf{MT}$ of affine symplectic varieties with Hamiltonian actions.

Moore–Tachikawa conjecture. There exists a two-dimensional TQFT

$$\eta_G:\mathbf{Cob}_2\longrightarrow\mathbf{MT}$$

satisfying $\eta_G(S^1)=G$ and assigning the cup cobordism to

$$[G\times\mathrm{Kos}].$$

This formulates the Moore–Tachikawa conjecture in the case where the target category is $\mathbf{MT}$ and the value on the circle is $G$. The supplied text does not state whether the conjecture has been resolved.