Can the kitchen sink waste pipe run from where it comes out of the concrete slab to the sink by running horizontally under the cabinet floor?
Horizontal - no.
No drain line is EVER horizontal. Unless someone was an idiot and should not have been plumbing....
Perfectly acceptable to run at an appropriate slope, however. 1/4&quot; per foot (or 2%) is the standard minimum slope for small drain lines like this.
How will you handle the venting? That is a complex process for island sinks, and if it was a peninsula before probably not arranged for. You mention having a &quot;wall behind&quot; - can your vent run through that (is your island not an island in the usual sense?)
There are ways far less drastic than a jackhammer to get into concrete and rearrange plumbing.