To the question of adding more expensive long-term assets in additional Worcester track capacity that would have to be financially justified in cost v. benefit v. competing use for other projects over a 25-year time horizon, that would be considered in long, strategic terms and beyond the shorter-term issues and observations continuing to be seen throughout this year.
The problem of trains sitting idle for days in Charlton (Westfield or elsewhere) has been a symptom, probably the most critical short of embargoing traffic with both seen elsewhere, of congestion caused by a shortage of qualified train & engine crews on CSX in New England and along their northern tier Baltimore-Selkirk-Buffalo, amplified by a much-widened variation in the flow of traffic caused by this and overall railroad network congestion, including amongst customers. Additionally, to some degree, the added demands caused by crew shortages on other New England railroads and in meeting important customer needs across CSX's various New England markets has added to the problem. So, a solution of adding more trainstarts or increasing the risk of re-crews is not the immediate answer, at the least until there's enough crews, and for a problem that in all likelihood will be short-term in the scheme of things, investment in new track is also not the answer.
As I see it, using Worcester as a hub to mix & match blocks of traffic to a balanced train operation, even if it requires hours-long use of main track, and supporting the new demand of an added car-handling-saving Westborough block amongst other blocks' requirements as well as the imbalanced westbound service demands of intermodal, all within the context of today's sophisticated network decision-making operating under strategically-beneficial PSR principles, made sense. When you think of the form & function of Worcester, it's not to classify individual cars into blocks (that's being done in Framingham and Selkirk), nor to provide the same amount of intermodal flatcar storage outside the intermodal yard as was once required. And, ex-Conrail east-of-Worcester carload merchandise traffic has been a net-same/negative with westward C&D waste traffic trending upwards but offset by eastbound traffic losses and with the closure of Beacon Park shifting traffic to a renewed-G&U and new Westborough transload, both created by the closure, changing traffic block/ing characteristics. In the shorter-run, beyond the challenging problem of congestion created by the crew shortage, looks to me like Worcester has enough track capacity to meet the existing demands without creating more trainstarts or adding new track.
Moving forward, the bigger, longer-term and more-important effects of probable further shifting in ex-Conrail east-of-Worcester traffic (to the G&U, southeast MA , up onto Pan Am (where I place my bets for the majority of it), or elsewhere?)) with 5-10 times the potential impact of trending C&D and other growth potential seen this year; CSX's Pan Am and Pan Am Southern purchase; and, a probable multi-billion dollar investment in passenger rail primarily Boston-Springfield will be the drivers of Worcester's future form and function within CSX's blocking and train operations. In this regard, I think a change in CSX train operations could likely be driven by an addition of the NS trackage rights intermodal train pair, if not before, and should there be investment in additional track it'll come from an East-West Passenger Rail Project as Taracer wrote.
As a couple of related asides, I recall when Worcester ~50 years ago required 4 yards each staffed with yardmasters and clerks and 10 daily yard crews consisting of 38 crewmembers to do what probably is roughly the same relative business as today, and, driving by a local national trucking company's terminal frequently during this period of tough area railroad congestion seeing the same kind of congestion with their daily inbound trailer loads sitting parked and untouched in their yard for the same reasons- not enough drivers and dock workers and uneven and surging freight flows (though probably no talk of adding linehaul runs or expanding the parking lot!).