Answer: R’ David Feinstein writes that his father, R’ Moshe Feinstein held that one should push oneself to drink wine, even if it causes him mild discomfort. R’ Zvi Pesach Frank (Mikraei Kodesh, Pesach 2:35) argues that a non-alcoholic beverage does not make one happy in the same way that wine does and therefore cannot be used on Seder night.
R’ Shlomo Zalman Auerbach, however, (Halichos Shlomo, Pesach 9:11) writes that grape juice has the same status as wine, as drinking grape juice also symbolises freedom.
If possible, one should at least dilute the grape juice with a little wine. (R’ Moshe Sternbuch, Teshuvos Vehanhagos, 2:243)
R’ Avrohom Blumenkrantz (Chasdei Avrohom 20) writes that one shouldn't use grape juice made from concentrate for kiddush or on Seder night.
The Rema (OC 453:1) writes that we are accustomed to only eating wheat matza. Therefore, non-wheat matza should only be eaten as a last resort, such as for health reasons.
R' Yitzchok Yaakov Weiss (Minchas Yitzchak 9:49) was concerned that oats become chametz quicker than wheat.
Spelt-matza is easier to digest, and presents less concerns than oats. One should not choose to eat Spelt-matza on Seder night, however, just because they prefer the taste.