why though? Can they hold it? 40km is within some artillery or mlrs range....
I guess they might also plan to take the coastline. I plotted range of some possible Ukrainian strike weapons to Snake Island. As seen the MLRS and Switchblades are coming from a relatively small plotline of coastal area, where Town of Vilkovne is. If Russians managed to secure Vilkovne, then it will put Switchblades and MLRS out of options. Only Tochka or TB-2's having the range for snake island aside from aircrafts or helos. which means putting some heavier system e.g Buk-M3 or even S-300 become feasible as risk of getting saturated by artillery are minimized. Those two will then provide ABM coverage for any Russian forces there from Tochka strike.
Town of Izmail is a special concern as it apparently have an airstrip. The TB-2 that previously strike Snake Island apparently take off and controlled from there.