Assuming that Minekura uses this part of the original Journey to the West, and assuming that this appearance isn't just Rule of Cool, art such as this depicting the Seiten Taisei could be really far in advance foreshadowing of what Goku/Seiten Taisei will become upon the end of the journey (see the last listing on The Other Wiki for details on Sun Wukong's becoming a Buddha). My reasons are thus: