The response was that the first thing to be shortened should be parts of נרצה (such as only singing the final summary paragraphs of אחד מי יודע and חד גדיא). In terms of מגיד, the advice was not to remove anything, although various parts could be recited in the local language in order to increase their interest. However, any brachot or parts of Hallel should remain in Hebrew, and any particular noteworthy segments of the seder [ed. - perhaps מה נשתנה] should be left in Hebrew so as to preserve the traditional flavor of the seder.
In terms of translating parts of the seder, in a footnote the repondents discuss three reasons why we are generally opposed to reciting davening in translation and why those reasons do not apply when it comes to the seder:
1) It is often difficult to translate davening in a way that accurately preserves the true meaning and intention of the prayer. However, by the seder we are not as concerned with the specific words as we are with telling the story. As such, discussing the story in a familiar language could actually be an improvement over reciting the written text.
2) The are various סגולות connected to the words of davening - again, this does not apply to מגיד, which is composed of various statements of חז"ל which were not originally written for the purpose of being combined into the seder.
3) The resistance to davening in a language other than Hebrew is partially rooted in a fear of emboldening reformist elements. When it comes to the seder, that fear is not so salient, as people have always read or discussed the Haggada in their own language.