Joseph, Chassidishe boys marrying Yeshivishe girls is not a trend, they are exceptions, which will continue to happen but I can guarantee you it will not become a trend, certainly not in the next 100 years unless Moshiach comes before and things may be different. These kind of marriages are not new, “neutral” Chassidim CAN BE (but are not necessarily) similar to Yeshivisha/Litvishe but with shtreimlach and have “intermarried” for decades. Also, if people have what some consider “issues” that are hard to surmount within their communities they can “marry out” if they care more about shidduchim than others’ shittas. But most Chassidim are not neutral and would never make such a shidduch and vice versa- the average Yeshivishishe, no matter the age, will not be seeking to marry a Chassidishe person.
Also for some for whom this has worked are those who do not follow their parents derech and become more “modern” in levush and custom and they are more open to mixing with different types. But also this type of mixing is few and far in between, it is more common for these people to find their other “modern” half with backgrounds like their own.