Pete Rose went from single A to the major leagues. My point? If you can play baseball you can play baseball. What Alonso possesses over most prospects is the thing that most prospects would require to play major league baseball. All major prospects have talent, what most lack is makeup and polish Alonso has a fair degree of both as did Rose. I'm not suggesting he would set the league on fire right away but what I am suggesting is that he could hold his own better than most players in single A, AA and some in AAA. I mean you have the majority of the board who thinks he is in AAA before the season is over. Why do they think that? They think it because he can play at that level right now. And another thing if his confidence were shook after a week or 2 in the majors regardless of the outcome he'd prove worthy of being dealt anyhow. I believe his confidence is too great to be broke over a couple of weeks anyway. You can also handle him taking offense by telling him up front that this is just a cameo and he'll be headed back or to AA once Votto returns. If he does well you keep him around if he doesn't he knew all along it was just a cameo and it's nothing personal.
I suppose Votto could feel alienated if he were to come back and not have his position. However who says he has too be? If Alonso is swinging the bat that well it get's dicey, and there are a few ways to handle it fairly and keep everyone happy. Remember we did tell Alonso that no matter what this was just a cameo, you have that to fall back on if all else fails. But he'd have to set the league on fire in order to make that an issue, it's posssible but not likely. I personally feel that if you handle it correctly you can pull it all off without hurting anything. I guess what I mean is I can see several scenarios that it can work out just fine for everyone involved and very few scenarios if any that it can turn out negatively. As far as your examples go I don't believe 1 & 2 are an issue and #3 could if it's not handled properly.