That's a nice find!
Although I don't know any IL instr which explicitly uses DS_Swizzle.
I was checked it, maybe other instructions are there and found some new undocumented gems (introduced whatever after cat11.12):
96bit, 128bit (continuous) DS_ instructions with one offset.
v_exp_legacy/log_legacy
v_floor/ceil/trunc for f64
s_cbranch_debug_system, s_cbranch_debug_user : Maybe this is windows's "int 3" one byte debug equivalent.
ds_wrap_rtn_b32 : another complex ds opetarion
v_mad_i64_i32 -> 64bit(32bit * 32bit) + 64.bit, now that's great for 64bit address arithmetic, I guess it takes only 4 cycles and is made of reusing some parts of the f64 unit. With mul_lo, mul_hi, add, addc it would take 10 cycles.
flat_* : Memory IO operations: I think it only needs a flat 64bit address, but IDK...