When will Apple get an Ipad with a built in Pencil holder?

Contributors here are all end-users, just like you. Other than information already published by Apple, nobody here has any insight into Apple’s product design decisions or future software development roadmap.

That said, consider that there are many third-party iPad cases specifically designed to store the Pencil with the iPad - and for iPad models that support the second generation Apple Pencil or Apple Pencil Pro, will allow the Pencil to optimally charge while docked with the host iPad.

OtterBox is one of the many options marketed by Apple. STMgoods is another manufacturer with excellent reputation, although there a many other third-party alternatives that can be found with a simple Google Search.

As to your comments concerning your iPad being scratched, cosmetic damage to the edge of the iPad can perhaps be expected if the touching surfaces of the iPad and Pencil are not kept clean of dust and dirt. Regular dust and grit present in many environments is abrasive - and when surfaces slide together, this abrasive material can cause damage to the anodised surface of the iPad frame. A little preventative care can completely avoid this type of damage before it occurs.

Other than the site Moderators, Apple neither monitor nor participate here. As such, if you hope to reach Apple through these forums, you will be disappointed. Apple does however invite submission of comments and feedback via its Product Feedback portal. For iPad and iPadOS:

Feedback - iPad - Apple

Clearly it is inevitable that adding a case to an iPad will always add a little bulk - but so would adding built-in storage for an Apple Pencil that is in almost all cases thicker than the iPad itself.

Unlike the plastic stylus of Samsung devices, an Apple Pencil is an active device that contains electronic components and a battery. Consider that an iPad has no empty internal space to house any kind of stylus - and as such the iPad would have to be made larger (or its battery reduced in size and capacity) to accommodate internal storage.

Assuming that you have a recent iPad Pro, the OtterBox cases marketed by Apple really do not add excessive bulk, but do add additional physical protection and captive Pencil storage.

Some other third-party option can add considerable bulk where they are intended for use in harsh environments - or situations where substantial drop or screen protection is warranted.

maybe if enough of people suggest it using their feedback channel

Product Feedback - Apple