First, Tafsir of Ibn Abbas and Al-Jalalayn unequivocally state this is about a wife, a child or a partner.

Tafsir Ibn Abbas:

"Then Allah revealed the following, when they said that the angels are Allah's daughters: (If We had wished to find a pastime) if We wished to have daughters; and it is said that this means: if We wished to have a wife; and it is also said that this means: if We wished to have children, (We could have found it in Our presence) from Us from among the maidens of Paradise (if We ever did) and We will never do this." (Tafsir Ibn Abbas)

"Had We desired to find some diversion, that which provides diversion, in the way of a partner or a child, We would have found it with Ourselves, from among the beautiful-eyed houris or angels, were We to do [so]. But We did not do so, thus We never desired it."

Tafsir Al-Jalalayn

It is interesting how a 21st century Muslim would give a Quranic verse an interpretation different from even the very companions of the prophet. Did the prophet not pray Allah to grant Ibn Abbas insight into the Quran? On what authority are you giving this interpretation now. Are you innovating?

Secondly, same Surah 21 verses 22 and 26 would seem to lend credence to the interpretation of Ibn Abbas that this is about partners and sons. Verse 22 says Allah is exalted above all they associate with him, verse 26 says "they claim Allah has begotten a son". So verse 17 would be an attempted refutation of the Christian belief.

Finally and still more importantly, even if I were to grant your interpretation over and above that of Ibn Abbas (who your prophet prayed for authoritative interpretation on the Quran) it still does not answer the "us" bit. Who is the "us" that Allah could distract himself with? Is there a royal "us" as well? And this does not make sense because a distraction, plaything or sport by definition would have to be something outside yourself, so what is outside this one Allah but within this one Allah that is capable of distracting him? The verse says Allah would have "TAKEN" it from among us not CREATED it from among us, so it definitely already exists and is not going to be created so your explanation flops in that regard.

We are skirting trinity territory here my friend.