The rationale: This should encourage group play. The XP per player decreases as the party size increases up until a group of 4, then starts to slowly increase up until a party of 7. When the party is full, there is a larger bonus to experience. The XP distribution should give a smoother transition between different party sizes, and makes it feel more rewarding to group up without making any specific party size too rewarding.
Why you should want this change: Rebalancing the distribution of XP benefits almost all aspects of the game:
• Makes the content difficulty of ROA and DD less daunting for new players. Level 175 is often seen as a "difficulty spike" as DD3-4 can be tough without decent gear. Changing the XP distribution would allow players to join smaller groups to farm this content without being "punished".
• Parties will no longer have to shout for hours on end, waiting for that last person to join a 7/8 powerlevel before they start.
• Promotes a more active gameplay style for smaller groups in dungeons, with potentially a lower reliance on powerleveling.
• No downside for solo players.
End notes: A change like this would "increase" the amount of experience given by a mob (when looking at base XP * number of players) although I don't believe it would make a material difference. The change is not fundamentally different to the current bonus of a full party, it is just spread differently across the number of players. The intent of this change would be to "artificially" make the leveling experience "faster" due to less down-time while waiting for parties to form, instead of "actually" making leveling faster due to more experience.