Currently the chain goes like this
NBLE > CO2 > OXYG > URAN > PLUT > SING
In my personal opinion going to something destructive is a good idea, but I think SING is too destructive to be the next in line. I feel the line would be a little better like this:
NBLE > CO2 > OXYG > URAN > PLUT > AMTR > SING
Antimatter is made in the LHC when colliding protons, so at least being able to create it makes sense.
Also, antimatter is still a destructive element, but not as insane as SING. I also feel that SING should be made at even higher speeds, while AMTR takes the place of SING.
Just my own thoughts. It would also be a way to actually make antimatter now.
But, I'm one voice of many, feel free to discuss what you think.