The question posed was that they think if people would not be strict to only marry within their own sect and group, it might solve the growing issue of older singles. For example, there are older Chassidishe men who have not yet found their match, and their are older Litvish or Sefardic women also not yet having found their match. If they could be set up to date each other, many of them might find their match and get married, but when a shidduch is presented from different communities and eidot, they are often rejected immediately. 

Because mixing and matching can lead to halachic questions, such as dealing with different minhagim, nusach of prayers, and the like, is this an issue to avoid as has been mostly done until now with people generally marrying only within their groups, or should an initiative be promoted to encourage people to date and marry people form other groups and eidot?

Rav Zilbershtein responded that the different minhagim and forms of service among different groups did not just form naturally over time but are related to the idea of the 12 tribes each with their own minhagim and mentality and style. Despite those differences in the tribes, Chazal say Tu Bshvat is a happy day because that is the day the tribes were allowed to marry into one another.

Ergo, nowadays as well - despite the differences, this is something we can overcome and halacha knows how to resolve all those questions that might come up. We have so much in common that it is a shame to focus on the minor differences and allow them to prevent people from building klal yisrael. It is a great mitzva to encourage this.

Beit Hillel and Beit Shammai also had differences yet they did not allow those differences to prevent them from marrying into each others families.

Interestingly, Rav Zilbershtein points out, that despite the differences and how different communities lived separately and in different places, the calendar year stayed the same among all the communities, with the holidays on the same days and shabbos and rosh chdesh, etc. Despite all the differences and developments, that all stayed the same. Rav Zilbershtein said that such a change would really have prevented people form marrying from other communities but Hashem helped us as a sign that he wants us all to be together and the differences we do have are minor.

source: Hamechadesh