This dynamic was discussed here before Story even agreed to join Boston. It could make for some awkward moments, or the three middle infielders -- including Cora -- could all respond as professionals and feed off the challenge. For all we know, Bogaerts could elevate his game, inspired by and competing with a new compeer. An extension before the opt out would also end any of that speculation.
The reason Sox fans think this is a good thing: 1) the club just got better, adding an all-around star who has power, speed and D, a 5.8 WAR per 162, with a better rate of extra-base hits on the road than even X; 2) it shows, finally, that Bloom will offer big money to individuals to improve the Sox... which leads to 3) there is now hope that Bloom will extend Red Sox homegrown stars, instead of dumping them for prospects and alienating the fanbase.