This past Sunday I attended Rav Simon's weekly halacha shiur where he is currently giving a series of shiurim on different aspects of saying the bracha shehechiyanu.
The topic of this particular shiur was saying shehechiyanu on acquiring/purchasing or receiving a new house or keilim (loosely defined here as vessels, but referring to certain items clothing, and other possessions of significance).
He mentioned an interesting point, one of many that he has heard during his many conversations with Rav Yitzchak Abadi. Rav Abadi felt that a woman receiving an engagement ring could, in fact say shehechiyanu on accepting the ring. The significance of that particular gift certainly brings the woman great simcha. In addition, from the standpoint of the wording of the bracha itself, certainly she is quite b'simcha to have finally reached the momentous day of receiving and accepting a marriage proposal (not to mention the ring)!
While ASoG didn't say a shehechiyanu when I popped the question (Rav Simon also wasn't clear if this was entirely lema'aseh or not), I hope others out there will get the opportunity to ponder this question as a practical application soon enough!