Ferruchemy and hemalurgy interactions

[Bautax]

What would happen if a ferruchemist or ferring got a spike containing a ferruchemichal ability (in the ferring's case it would contain his ability).

Would it improve the storing capabilities making it no longer end neutral? Or would it have another effect

[+Artemos he/him]

I doubt it would no longer make it end neutral. Most likely, it would simply strengthen the feruchemist's ability to use feruchemy - similar to how a mistborn burning lerasium only increases their strength.

[Scion of the Mists]

I don't think that it's been directly answered, but the main theory I've seen is that it would improve your store/tap rate (similar to duralumin).  So it would still be end-neutral (i.e. you'd still get out what you'd put in), but you'd be able to do it faster.  

[+Lewis Nethur He/Him]

It's also speculated that instinctive control over the power would be improved. IE: they could more precisely control their store/tap rate to meet their needs with less focus. Another theory, that has been RAFO'd as I recall, is that selective storing/tapping could become possible with great enough skill/power in feruchemy. For example, storing sight from only one eye or tapping strength in only one arm.