Herculez Gomez to MLS rumors generally lack time frames, but when Grant Wahl appeared on Fox Soccer earlier today the time frame was clear - the Summer Transfer Window. Also clear were the interested MLS teams - Seattle Sounders FC and Toronto FC. There are challenges.
Sporting Kansas City holds the MLS rights to Herc because they made an offer at the time that was on the edge of fair value, but has long since been surpassed as Gomez dominated in Mexico. There is also the case that the Sounders have three Designated Players right now. One of those would need to move on if Gomez were to break over the 400k$ salary realm (he like should). It is believed that both Shalrie Joseph and Mauro Rosales are under DP contracts for this year only so there may be accounting judo available with the support of the league to get one of the more marketable United States National Team players back into MLS.
The other 'problem' is that Seattle has two forwards. With MLS' roster limits and cap structure it would not make sense to have one of Obafemi Martins, Eddie Johnson and Herculez Gomez on the bench. Maybe the accounting judo includes a sale of one of the other two.
Herculez has a history in Seattle. It is one that has been renewed through the two CCL meetings between Santos Laguna and the Sounders. He gets along with the fanbase, as well as the ownership (link 1, 2) and former teammates.
In under four years down in Liga MX he's slapped in more than 40 goals in all club competitions. Generally a forward Gomez has also played a very high winger and even spotted in the center on rare occasions.
A move like this would be big, aggressive and complicated. It is also clearly just a rumor at this time, though from a reporter who is generally in the know on these types of things.