I never heard back. Maybe they underestimated how many people would submit.
Don't give up! This is the e-mail I received when I submitted on 15th August (bolding mine):
Many thanks for your submission to Open House. Please note that due to the enormous number of submissions we are receiving we have had to extend our response-by date slightly. We will reply within four to six weeks of receiving your submission but
we will be in contact with everybody. We look forward to reading your work. With kind regards, United Agents.
Eight weeks have passed, but I ain't giving up until I get that e-mail response!
ETA: Someone on an author loop I'm part of just had a rejection from an ms submitted on 1st August (today is 18th October). As for me, I haven't finished writing the book I pitched (only the first three or four chapters) and I probably won't get around to giving it top priority unless they write back with interest.