Is that the coat of arms of Phillip II when married with Mary Tudor?
And yes, it would be cool. But it would not fit the reality in early Middle Ages, X-XIIIth Centuries, where this kind of division in coats of arms was not common.
What was common was to keep the most prestigious coat of arms (like the Hohenstaufens did, taking for themselves the three lions of Swabia), to keep your own families' one (what the House of Savoy did) or to integrate new coats of arms directly into your old one.
The last one was quite common in the X-XIth Centuries. Aragon, for instance, had initially less bars, for each of those bars represented a golden sceptre for each of the counties the original Counts of Barcelona held (Cerdanya, Barcelona and Girona). That's one of the theories that circulate about the controversial origin of the Aragonese coat of arms (Aragonese claim it to be of pure Aragonese origin, Catalans claim it to be originated in the House of Barcelona, which would eventually rule over Aragon, hence the problem... we'll never know with all those nationalisms around).
The Plantagenet coat of arms is also a proof of dynamic coat of arms. The CoA of Normandy and Aquitaine suggests that initially the dukes of Normandy had one single lion passant. Later, with Henry II, another lion would have been added, to represent Aquitaine. Whether the lions were passant or rampant, facing one each other, is not yet uncovered. And with Richard the Lionheart, a third lion was added. I don't know why, really, but an interpretation could be: England, Normandy and Aquitaine.
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Also, it would be really cool that you could add features to your coat of arms, to represent cadet branches. Go to Wikipedia and look for "brisures" or "cadency". Things like bordures, crossing bars, labels, saltires and other features can be very cool. French Capetian kings did it all the time:
http://fr.wikipedia.org/wiki/Brisure
http://es.wikipedia.org/wiki/Brisura